When you alter a symmetric key by dropping a non-existent password in Microsoft SQL Server 2008 R2, the symmetric key is closed unexpectedly. Additionally, you receive the following error message:
Msg 15315, Level 16, State 1, Line 1
The key 'symmetric key' is not open. Please open the key before using it.
This issue occurs because the modified date of the symmetric key is not updated in the cached copy after you update the symmetric key.
Cumulative update information
Cumulative Update 6 for SQL Server 2008 R2 Service Pack 2
The fix for this issue was first released in Cumulative Update 6. For more information about how to obtain this cumulative update package for SQL Server 2008 R2 Service Pack 2, click the following article number to view the article in the Microsoft Knowledge Base:
2830140 Cumulative update package 6 for SQL Server 2008 R2 Service Pack 2Note 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 Service Pack 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
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.