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SQL Server error 18456 means the server rejected a login. The client message is deliberately generic, so don’t assume the password is wrong: check the SQL Server error log for the failed login’s state and reason, then use the matching fix.
What SQL Server error 18456 means
Error 18456 is a login failure, not necessarily a network connection failure. SQL Server limits the detail shown to an unauthenticated client; the server’s error log is the more useful diagnostic source. The SQL Server Team put it this way: “The key to the message is the ‘State’ which the server will accurately set to reflect the source of the problem.” (SQL Server Team article, originally published in 2006 and republished in 2019.)
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How to find the server-side reason
- Open the SQL Server error log for the instance that rejected the connection. In SQL Server Management Studio, inspect the log through the server’s management interface, or open the error-log file using an authorized method.
- Find the entry corresponding to the failed login. Match its time and login name to the client attempt.
- Read the state and accompanying reason, then follow the relevant remedy below. State descriptions are diagnostic clues, not a universal mapping guaranteed to cover every SQL Server version or hosting environment. Consult the documentation for your version and the actual log entry.
State 1 is not a diagnosis on its own. Microsoft describes it as unavailable error information; often, the caller does not have permission to receive further details. Use the server log rather than treating state 1 as proof of a particular cause. See Microsoft’s Error 18456 reference.
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Four ways to fix error 18456
1. Verify the login, password, and login status
Check that the username in the connection attempt is correct, the password is valid, and the SQL Server login is enabled. Microsoft lists invalid user IDs, invalid passwords, and disabled logins among the causes associated with Error 18456 states. Correct the specific credential or account issue indicated by the log; repeatedly changing passwords without confirming the login name or status may not help.
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2. Match the authentication method to the account and instance
Use an authentication method supported by both the account and the SQL Server instance. For example, a Windows account submitted as a SQL Server Authentication login can fail. Conversely, a SQL Server login cannot authenticate if the instance is configured for Windows Authentication only.
Check the log and the instance’s authentication configuration before changing settings. If SQL Server and Windows Authentication mode is required and you are authorized to change the instance, enable it; otherwise, use an appropriate Windows login or request the necessary change from the instance administrator. Enabling SQL Server Authentication is not a blanket fix for every 18456 error.
3. Check the requested database and the login’s access
If the failure names a requested database, confirm that the database name in the connection string is correct and that the database is available. Then verify that the login has permission to access it. Microsoft identifies an incorrect database name, an offline database, and insufficient permissions as possible causes.
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1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsCorrect the connection string if it requests the wrong database. If the database is unavailable or the login lacks access, an authorized database administrator must address that condition; changing a password will not resolve a database-access failure.
4. Use the state and reason to choose the specific remedy
The error-log entry narrows the failure to the relevant category: credentials or login status, authentication-mode mismatch, or access to the requested database. Follow the cause shown there instead of applying unrelated changes. Microsoft’s state descriptions can help interpret the entry, but check guidance for your SQL Server version and hosting environment rather than assuming a single state list applies everywhere.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When the problem is not error 18456
If the client cannot reach the server or instance at all, investigate connectivity separately. A network or instance-specific failure is different from a server rejecting a login. Microsoft recommends connection tests and protocol checks to distinguish transport problems from login authorization issues; see its SQL Server connection troubleshooting guide.
For broader authentication troubleshooting, Microsoft also documents common causes in its overview of SQL Server authentication issues.
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