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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Repair Windows errors before they cause bigger problemsFix Now →“The pipe has been ended” is usually a symptom, not the root cause. In the documented ASP.NET/IIS case, NReco.PdfGenerator lost communication with its external wkhtmltopdf.exe renderer after that process failed. The server’s Windows event log identified an executable fault involving MSVCP120.dll (exception code 0xc0000135).
Start with the child-process fault, then verify IIS process architecture and native runtime dependencies. Do not begin by changing random NReco settings or copying DLLs from another computer. The steps below separate what the historical report established from prudent, general IIS isolation work.
What the error actually tells you
NReco’s HtmlToPdfConverter.GeneratePdfInternal communicates with a separate rendering executable. If that executable exits, crashes, cannot load a native module, or is terminated before NReco finishes reading and writing through the pipe, the managed code can surface “The pipe has been ended.” The wording describes the failed communication channel; by itself it does not identify whether the cause was a missing DLL, wrong bitness, permissions, a bad input page, or another process failure.
A Stack Overflow question, asked on April 22, 2015 and modified August 2, 2017, records this exact local-versus-server pattern. The report names wkhtmltopdf.exe version 0.12.2.1, an MSVCP120.dll fault, and exception code 0xc0000135. One answer says enabling a 32-bit application configuration and installing the matching 32-bit C++ runtime fixed that deployment; another answer says the asker made msvcp120.dll and msvcr120.dll available in the application’s bin directory. Those are individual historical workarounds, not current vendor instructions. See the original report at Stack Overflow.
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| Evidence | What it supports | What it does not prove |
|---|---|---|
Pipe exception from GeneratePdfInternal |
The renderer communication ended unexpectedly. | It does not name the underlying failure. |
Windows event log names wkhtmltopdf.exe and MSVCP120.dll |
The external process failed while loading or running a native dependency in that case. | Every installation has the same missing module. |
| 32-bit runtime fixed the reported 32-bit deployment | Worker-process and dependency architecture must match. | Switching every server to 32-bit is universally correct. |
| DLLs placed in the application directory resolved the asker’s issue | The process could then locate the required files in that environment. | Blindly copying DLLs is a supported deployment policy. |
Fast diagnostic sequence
- Capture the complete failure. Save the full exception, inner exception, URL or HTML input, NReco configuration, and timestamp. The pipe text is less useful than the first child-process error.
- Check the server’s Application event log. Look for an error at the same time as the request. Record the faulting executable, module name, exception code, and any “side-by-side” or loader message.
- Identify the actual worker-process bitness. Check the IIS application pool’s Enable 32-Bit Applications setting and confirm that the running worker process matches it. A 64-bit Windows installation can run a 32-bit application pool.
- Verify the native runtime for the deployed renderer. Install the supported runtime architecture required by the executable and your deployment policy. Do not infer the requirement from the operating system’s bitness alone.
- Retest with a minimal input. Use a simple, known-good HTML page on the same server. This separates process startup problems from page-specific JavaScript, fonts, network calls, or malformed markup.
- Run under the real IIS identity. A successful test from Visual Studio or an administrator account does not prove that the application-pool identity can execute the renderer or write to its temporary and output locations.
1. Inspect Windows event logs before changing settings
Open Event Viewer and go to Windows Logs → Application. Filter or sort around the request time, then inspect entries whose source is an application error, Windows Error Reporting, or a loader-related service. Record:
- the faulting application, such as
wkhtmltopdf.exe; - the faulting module, such as
MSVCP120.dll; - the exception code (the historical report shows
0xc0000135); - the executable path and, if shown, the process architecture; and
- any message that names a missing or incompatible assembly or runtime.
Also enable whatever NReco or application logging you already use so that the renderer’s exit information and standard error are retained. If Event Viewer shows no child-process fault, treat that as an unresolved branch rather than proof that the renderer is healthy: check the application log, process permissions, antivirus events, and the exact executable path next.
2. Match IIS architecture to the renderer and runtime
Check the application-pool setting
In IIS Manager, open Application Pools, select the pool serving the site, choose Advanced Settings, and inspect Enable 32-Bit Applications. Compare that setting with the architecture of the wkhtmltopdf.exe shipped with the application and with the native runtime installed for it.
The historical accepted answer describes a 32-bit application running on a 64-bit server. Installing the 32-bit C++ runtime and running the site in the required 32-bit mode solved that user’s failure. Apply the same reasoning to your deployment, but confirm the executable and dependency requirements first. A 64-bit worker cannot load a 32-bit in-process native dependency, and enabling 32-bit mode is not a general repair for a genuinely 64-bit renderer.
Confirm the process you are actually testing
Recycle the relevant pool after changing architecture, then reproduce one request. Use Task Manager’s Details view or your approved process-monitoring tool to verify that the expected worker process and renderer are being launched. If multiple sites or pools use different copies of wkhtmltopdf.exe, check the path for the failing site instead of assuming they share one installation.
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3. Resolve native dependency failures safely
Names such as MSVCP120.dll and msvcr120.dll point to native C/C++ runtime files. The historical report says those files were made accessible from the application’s bin directory, but that is not a universal recommendation. Copying an arbitrary DLL downloaded from the web can introduce an incompatible or tampered binary and can leave servicing unclear.
- Identify the exact executable that failed and the architecture it requires.
- Use the supported Microsoft or organizational software-distribution channel for the corresponding runtime, matching the required architecture.
- Install it under your normal server change-control process, then recycle the application pool.
- Only use application-local deployment when the runtime vendor and your application’s deployment policy explicitly support it; document the file version, source, and servicing owner.
- Retest and verify that the event log no longer reports the loader failure.
If the event log names a different module, troubleshoot that module rather than adding the two DLL names from the old report. A missing font, graphics library, or another native component can produce the same high-level pipe symptom.
4. Separate renderer startup from page-content failures
Use a minimal local page
Create a tiny HTML file or data string containing plain text and no external resources. Generate a PDF from that input on the server under the same application identity. If it fails before any page content is involved, concentrate on process launch, architecture, dependencies, permissions, and temporary directories.
Add complexity one variable at a time
When the minimal case succeeds, add the real URL, stylesheets, images, fonts, JavaScript, authentication headers, and redirects incrementally. A page that never finishes loading, requires an unavailable network route, or triggers renderer-specific JavaScript can fail after the process starts. Capture the exact input and the step at which the failure returns.
Check URL and resource reachability from the server
“Works in my browser” may mean the developer’s workstation can resolve a hostname or access an authenticated resource that the IIS server cannot. Test DNS, proxy rules, firewall egress, TLS trust, and application authentication from the server’s network context. Keep this branch separate from a loader error shown in Event Viewer.
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5. Verify identity, paths, and temporary storage
These are general IIS checks rather than conclusions from the cited Stack Overflow case. Confirm that the application-pool identity can:
- execute the deployed
wkhtmltopdf.exeand read its adjacent files; - read templates, CSS, images, fonts, and any custom configuration;
- create and delete temporary files in the directory used by NReco or the application; and
- write the final PDF to the destination selected by your code.
Use absolute, known paths while diagnosing. Log the resolved executable path, current working directory, temporary directory, and output path. Avoid granting broad write access to the entire site directory; grant only the minimum rights to dedicated folders and then remove diagnostic permissions that are no longer needed.
Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problems6. Retest under production-like conditions
After correcting a dependency or architecture mismatch, recycle the pool and make several requests using the same site binding, identity, environment variables, and input that failed. A test from an elevated console can hide permission problems. Keep the event-log entry, renderer version, runtime package version, pool architecture, and result together in the deployment record so a later server rebuild can reproduce the working state.
If failures occur only under concurrent load, capture timestamps and process IDs and check whether the renderer is being terminated by pool recycling, an antivirus policy, a job timeout, or resource exhaustion. Do not “fix” that pattern by indefinitely increasing request timeouts; first establish whether the child process is crashing or being deliberately stopped.
Common scenarios and the next check
| Symptom | Most useful next check | Safe response |
|---|---|---|
| Works locally, fails immediately on IIS | Application event log and renderer path | Find the child-process fault before changing PDF options. |
| Event log names a runtime DLL | Worker and executable architecture; installed runtime architecture | Install the supported matching runtime through normal change control. |
| Minimal HTML fails too | Launch permission, executable path, temp directory, native dependencies | Keep page-content debugging out of this branch. |
| Minimal HTML succeeds but the real URL fails | Server-side DNS, proxy, TLS, authentication, resources, and scripts | Add inputs incrementally and log the first failing resource. |
| Only one pool or site fails | That pool’s bitness, identity, environment, and executable copy | Compare configuration with a working site rather than the whole server. |
| Failure appears during deployment changes | Pool recycle, antivirus, file lock, and package contents | Check deployment and security logs for a process termination. |
What not to do
- Do not treat the pipe wording as a diagnosis or repeatedly retry it without collecting the child-process error.
- Do not switch the entire server to 32-bit mode without confirming which executable and runtime require it.
- Do not download DLLs from an unknown site or replace system files by hand.
- Do not compare only with a developer workstation; compare identities, paths, architecture, runtime packages, and network access.
- Do not claim that the historical
wkhtmltopdfversion is a current recommendation. The0.12.2.1number belongs to the 2015 report.
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Keep the renderer package and native runtime under version control or an auditable installer process. Log a correlation ID, input type, renderer exit status, elapsed time, and output size for each job, while excluding secrets and sensitive HTML. Use a bounded queue if PDF work can arrive in bursts, and set a finite cancellation policy so a stuck renderer cannot consume every worker thread. Monitor failed child-process launches separately from page-level failures; they require different remediation.
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Because no current official NReco troubleshooting page for this exact message is established here, verify the supported NReco and wkhtmltopdf packaging for your edition before standardizing a runtime or version. The evidence above is strongest as a diagnostic model: find why the external process ended, then correct that specific cause.
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