Symptoms
Assume that you have an instance of Microsoft SQL Server 2008 or Microsoft SQL Server 2008 R2 that is configured to use a case-sensitive collation. You try to add a Microsoft Windows NT user or group as a login to SQL Server by using one of the following methods:
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You use SQL Server Management Studio (SSMS).
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You use a sp_grantlogin system stored procedure.
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You use a CREATE LOGIN statement.
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You use a SUSER_SID function.
In this situation, you receive the following error message:
Error 15401 Windows NT user or group 'Domain_name\User_name' not found.Check the name again.
Cause
This issue occurs because the login that the Windows NT API returns is case-insensitive. However, SQL Server performs a case-sensitive comparison because of the case-sensitive collation that you configured.
Resolution
Cumulative update information
Cumulative Update 4 for SQL Server 2008 R2 SP2
The fix for this issue was first released in Cumulative Update 4. For more information about how to obtain this cumulative update package for SQL Server 2008 R2 SP 2, click the following article number to view the article in the Microsoft Knowledge Base:
2777358 Cumulative update package 4 for SQL Server 2008 R2 Service Pack 2 Note Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2008 R2 SP 2 fix release. We recommend that you consider applying the most recent fix release that contains this hotfix. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
2730301 The SQL Server 2008 R2 builds that were released after SQL Server 2008 R2 Service Pack 2 was released
Cumulative update package 10 for SQL Server 2008 R2 Service Pack 1
The fix for this issue was first released in Cumulative Update 10. For more information about how to obtain this cumulative update package for SQL Server 2008 R2 SP1, click the following article number to view the article in the Microsoft Knowledge Base:
2783135 Cumulative update package 10 for SQL Server 2008 R2 SP1 Note Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2008 R2 SP1 fix release. We recommend that you consider applying the most recent fix release that contains this hotfix. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
2567616 The SQL Server 2008 R2 builds that were released after SQL Server 2008 R2 Service Pack 1 was released
Cumulative update 8 for SQL Server 2008 Service Pack 3 (SP3)
The fix for this issue was first released in Cumulative Update 8. For more information about how to obtain this cumulative update package for SQL Server 2008 Service Pack 3, click the following article number to view the article in the Microsoft Knowledge Base:
2771833 Cumulative update package 8 for SQL Server 2008 Service Pack 3Note Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2008 Service Pack 3 fix release. We recommend that you consider applying the most recent fix release that contains this hotfix. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
2629969 The SQL Server 2008 builds that were released after SQL Server 2008 Service Pack 3 was released
For more information about how to troubleshoot error 15401, go to the following Microsoft Knowledge Base article:How to troubleshoot error 15401
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
