Login error

[Microsoft][ODBC SQL Server Driver][SQL Server]Login failed for user 'abcdef'. - SQLSTATE: 28000.

When I googled for it, experts and microsoft link recommended to change SECURITY to MIXED MODE and restart but when I checked for security it is already set in MIXED MODE, now please help me how to trouble shoot it.

here are the links:

http://dba.stackexchange.com/questions/29992/odbc-data-source-sql-server-connection-login-failed-for-user

https://support.microsoft.com/kb/555332?wa=wsignin1.0.

SQL Version is : Microsoft SQL Server 2005 - 9.00.5000.00 (Intel X86)   Dec 10 2010 10:56:29   Copyright (c) 1988-2005 Microsoft Corporation  Standard Edition on Windows NT 5.2 (Build 3790: Service Pack 2) 

Please help me in getting this resolved.

Thanks in advance.