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CAA2000B is a Microsoft Teams sign-in symptom, not a diagnosis. It does not automatically mean your password is wrong or your cache is corrupted. First try Teams on the web and capture any longer AADSTS error, correlation ID, and timestamp. If web sign-in works, focus on the desktop app and device; if it fails too—or other people are affected—your account, organization’s policies, or a Microsoft service may be involved.
What CAA2000B means—and what to check first
Teams displays CAA2000B when sign-in fails, but Microsoft’s public sign-in guidance does not assign this code one universal cause. The accompanying server message may point to an account or MFA problem, a Conditional Access rule, device compliance, an application setting, a network issue, or local Teams authentication data. Microsoft’s Teams sign-in guidance treats status codes as diagnostic clues and advises contacting an administrator when a sign-in problem remains unresolved.
Before changing settings, write down the code and any longer AADSTS code, full message, correlation or request ID, and the time of the failed attempt with its time zone. Note whether it fails in desktop Teams, Teams on the web, or other Microsoft 365 apps, and whether coworkers are affected. These details help an administrator find the corresponding event in Microsoft Entra sign-in logs.
Use web sign-in to narrow down the cause
Open the official Teams web client in a private or incognito browser window and sign in with the intended work or school account. Microsoft recommends comparing web and desktop sign-in when Teams cannot reconnect; see its Teams reconnect troubleshooting.
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| What happens | Where to investigate |
|---|---|
| Web works; desktop fails | Teams app state, account selection, installation, or device authentication. |
| Web and desktop fail for one user | Account status, password, MFA, license, device requirements, or Conditional Access. |
| Several users fail at once | Microsoft 365 service health, tenant policy or application settings, or a shared network change. |
| Web works only in a private window | Browser cookies, extensions, or an old web session. |
| Failure occurs only on one network or with VPN | VPN, proxy, firewall, DNS, TLS inspection, or network policy. |
| Other Microsoft 365 desktop apps fail too | Shared Microsoft authentication or device identity, rather than Teams alone. |
Try low-risk sign-in and device checks
Confirm the account and finish authentication
- Sign out of Teams if you can, quit the app, then reopen it.
- Choose the organization’s work or school account and verify the email address and tenant. Do not select a personal Microsoft account by mistake.
- Complete any password-change, MFA, security-verification, or device-registration prompt. If you recently changed your password, use the new password when asked to sign in again.
- If browser sign-in also fails, stop repeated retries and ask your organization’s administrator to check the account and sign-in event.
Teams uses modern authentication, which can involve single sign-on, MFA, and organization-specific policies. A missed or incomplete challenge can therefore look like an app error; the Microsoft sign-in guidance explains that authentication can depend on these organization settings.
Check time and network
- Turn on automatic date, time, and time-zone settings and correct any clock drift.
- Confirm other websites load. If your organization requires VPN, connect before starting Teams; if the VPN is optional, test the approved alternative network.
- Where company policy allows, test whether a proxy or TLS-inspection tool is interfering. Do not permanently disable endpoint protection or firewall controls as a general fix.
Incorrect device time can interfere with secure authorization. Microsoft’s reconnect guidance also identifies internet connectivity, VPN, proxy, firewall, and network interruptions as troubleshooting factors.
Quit Teams completely and reopen it
- Right-click the Teams icon in the taskbar or notification area.
- Select Quit, rather than merely closing the window.
- Start Teams again and retry sign-in.
Repair the local Teams app
Windows: try Repair, then Reset if available
- Open Settings > Apps > Installed apps.
- Find Microsoft Teams and open Advanced options.
- Select Repair first, then reopen Teams and test sign-in.
- If Repair does not help, use Reset and sign in again.
Windows and Teams package versions can use different labels or may not expose these options. Reset can remove local app data and require you to authenticate again; it does not correct an account block or tenant policy.
Clear cache only for the applicable Teams client
Microsoft’s published cache paths are for the documented Teams cache layout. Do not treat them as universal locations for every current Teams package.
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Classic Teams on Windows
- Quit Teams completely.
- In File Explorer’s address bar, enter
%appdata%MicrosoftTeams. - Delete the contents of that folder, then restart Teams and sign in.
Teams on macOS using the documented path
- Quit Teams.
- Delete
~/Library/Application Support/Microsoft/Teams. - Restart Teams and sign in.
Microsoft says clearing the cache does not uninstall Teams, but it can remove locally stored cache data such as icons, thumbnails, local message history, display images, and add-ons. This is local cached data, not a way to repair an account or policy block. For current Teams versions, use the available Windows Repair/Reset option or Microsoft’s reinstall process rather than deleting arbitrary folders. See Microsoft’s cache and reconnect instructions.
Reinstall Teams if the desktop client still fails
- Uninstall Teams.
- In File Explorer, open
%appdata%Microsoftand delete the Teams folder if it exists. - Download and reinstall Teams. If possible, run the installer as an administrator.
- Open Teams and try signing in again.
Microsoft lists this process in its Teams sign-in error troubleshooting. It may help with a damaged local installation, but will not fix invalid credentials, a disabled account or application, a missing entitlement, Conditional Access, or an outage. Do not remove unrelated Microsoft identity folders without IT guidance. On a managed device, company software management may reinstall Teams automatically.
If Teams on the web also fails
When the browser fails with the same account, prioritize identity and organization checks rather than repeatedly clearing the desktop cache:
- Account and password: Confirm the work or school account is active and that the new password is being used after a recent change.
- MFA and security verification: Complete all prompts and check whether the user is blocked from registering or satisfying the required method.
- Device and location: A policy may require a compliant or organization-joined device, a particular client, MFA, or an allowed network.
- Entitlement and tenant: Ask the administrator to confirm the expected Teams service entitlement is assigned and active. Requirements depend on account type and subscription; do not infer a missing license from CAA2000B alone.
- Service health: If more than one user is affected, check Microsoft 365 service health and recent tenant or network changes.
If only browser Teams fails, try a private window, disable interfering extensions for a controlled test, and check that browser cookies or an old session are not preventing sign-in. Microsoft’s reconnect guidance also suggests checking ad blockers for Teams on the web.
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Administrator checks: find the underlying sign-in failure
Run the Teams sign-in diagnostic
A Microsoft 365 administrator can use the Teams Sign-in diagnostic described in Microsoft’s sign-in error procedure. It requires an administrator account and is not available in every cloud or government environment. Provide the affected username, tenant, full error, correlation or request ID, timestamp and time zone, client and version, operating system, web-test result, and number of affected users.
Inspect Microsoft Entra sign-in logs
In the Microsoft Entra admin center, go to Entra ID > Monitoring & health > Sign-in logs. Filter by username, application, failed status, and time range; use the correlation ID if available. Open the matching event and inspect the failure reason, additional details, sign-in error code, authentication details, device information, Conditional Access results, and resource. Microsoft’s sign-in error troubleshooting guide identifies the correlation ID, error code, failure reason, username, and sign-in identifier as useful diagnostic details. A Reports Reader role is the least-privileged role referenced for viewing these reports, subject to tenant permissions and licensing.
Use the full AADSTS code and server message as the main diagnostic key. CAA2000B alone is not enough to identify why the request failed.
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Open the failed event’s Conditional Access tab to see whether a policy blocked the request. Check requirements for compliant or joined devices, approved clients or Intune app protection, MFA or authentication strength, location, risk, and platform. Confirm which user, application, resource, and device platform the policy targets, and whether a recent change explains the failure. Microsoft documents these checks and the What If tool in its Conditional Access troubleshooting guidance.
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Teams may request access to dependent Microsoft 365 resources, so a failure shown during Teams sign-in can involve a resource such as SharePoint or another service. Do not disable Conditional Access globally to test a single failure: broad policies can lock out users and administrators. Follow the tenant’s approved recovery or break-glass procedure when investigating a possible policy lockout.
Check application enablement only when the error points there
A historical Microsoft Q&A case connects CAA2000B with the more specific AADSTS7000112 message indicating that the Microsoft Teams application was disabled. This is one reported case, not the definition of CAA2000B; see the Microsoft Q&A example.
If the full error or sign-in logs indicate an application-disabled condition, an authorized administrator can open the Microsoft Entra admin center, go to Enterprise applications, find Microsoft Teams, and check its application properties and user sign-in enablement. Do not change this setting based on CAA2000B alone.
Check licensing, dependencies, and service status
Confirm that the user has the expected active entitlement and service plan, that the tenant is not restricted or suspended, and that the relevant Microsoft 365 services are healthy. Inspect the resource involved in the failed event: the blocked service may be a dependency requested during Teams authentication, not Teams itself. Use the error details and Conditional Access results to identify the affected resource before changing tenant configuration.
When to contact IT or Microsoft Support
Contact your organization’s IT administrator if web sign-in fails, the AADSTS message points to a policy or account block, other Microsoft 365 apps fail, or several users are affected. Include the exact error and full message, correlation/request ID, timestamp and time zone, username and tenant, device OS, Teams version and client type, whether web sign-in works, affected networks or VPN status, and the number of users affected. Administrators can use those details to locate the event, run the available diagnostic, and escalate to Microsoft Support with relevant logs if needed. Microsoft’s Teams troubleshooting guidance advises collecting debug logs and the sign-in-screen error code when local steps do not resolve the issue.
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