Trying to recover some disk space by shrinking the size of our WSUS database, or at least figure out why it's so big, I tried to connect to the Windows Internal Database in SQL Server Management Studio (using the \.\pipe\mssql$microsoft##ssee\sql\query database name I've seen referenced in multiple places) and got an error:
Cannot connect to \.\pipe\mssql$microsoft##ssee\sql\query.
Login failed for user '[ourdomain]/[myusername]'. (Microsoft SQL Server, Error: 18456)
Server Name: \.\pipe\mssql$microsoft##ssee\sql\query
Error Number: 18456
Line Number: 65536
My account has domain administrator privileges, so I don't understand why it wouldn't work. The help link it gives me says that "If your error indicates state 1, contact your SQL Server administrator" (who, unfortunately, is me).
I also tried the WsusDBMaintenance script from here, which should apparently just work, and got the same "Login failed for user" message.
Update: I found the corresponding entries in the error log, which say:
2009-10-09 14:13:51.30 Logon Error: 18456, Severity: 14, State: 11. 2009-10-09 14:13:51.30 Logon Login failed for user '[domain]\[user]'. [CLIENT: <named pipe>]
It says here that state 11 = "Valid login but server access failure".