sp_cycle_errorlog

Closes the current error log file and cycles the error log extension numbers just like a server restart. The new error log contains version and copyright information and a line indicating that the new log has been created.

Every time SQL Server is started, the current error log is renamed to errorlog.1; errorlog.1 becomes errorlog.2, errorlog.2 becomes errorlog.3, and so on. sp_cycle_errorlog enables you to cycle the error log files without stopping and starting the server.

http://technet.microsoft.com/en-us/library/ms182512%28v=sql.100%29.aspx

Understanding "login failed" (Error 18456) error messages in SQL Server 2005

Got login errors in the SQL Server 2005 databases. The following link solves the issue.

Understanding "login failed" (Error 18456) error messages in SQL Server 2005

If the server encounters an error that prevents a login from succeeding, the client will display the following error mesage.

Msg 18456, Level 14, State 1, Server , Line 1
Login failed for user ''

Note that the message is kept fairly nondescript to prevent information disclosure to unauthenticated clients.   In particular, the 'State' will always be shown to be '1' regardless of the nature of the problem.  To determine the true reason for the failure, the administrator can look in the server's error log where a corresponding entry will be written.  An example of an entry is:

2006-02-27 00:02:00.34 Logon     Error: 18456, Severity: 14, State: 8.

2006-02-27 00:02:00.34 Logon     Login failed for user ''. [CLIENT: ]

n

The key to the message is the 'State' which the server will accurately set to reflect the source of the problem.  In the example above, State 8 indicates that the authentication failed because the user provided an incorrect password.  The common error states and their descriptions are provided in the following table:

 

ERROR STATE	ERROR DESCRIPTION
2 and 5	Invalid userid
6	Attempt to use a Windows login name with SQL Authentication
7	Login disabled and password mismatch
8	Password mismatch
9	Invalid password
11 and 12	Valid login but server access failure
13	SQL Server service paused
18	Change password required