We have 2 failover servers and one client in our test environment. We have all the three configured in mixed mode authentication(windows + sql server authentication). But when we are failing over from 1st server to 2nd one, we are getting the following error message, 'Unable to connected to server xxxx: Server : Msg 18452, Level 16, State 1 [Microsoft][ODBC SQL Server Driver][SQL Server]Login failed for user 'null'. Reason: Not associated with a trusted SQL server connection.' I got some clue. For instance we have ser1(active) and ser2(passive) as clusters. I registered both in the client's EM. Now what I did was, I made ser1 to run and stopped sql service in ser2 (active/passive) through failover. Now in the client's EM I'm able to open ser1 and I cannot access ser2. Now what I did was, I failed over to ser2 ( so sql service in ser1 is stopped). But now I can still be able to access ser1 and also I can access ser2, even I'm able to open query analyzer in ser1 through EM.But when I try to open query analyzer directly, it is giving the same error message. ser1 is the virtual name given to both ser1 and ser2. So I think when connecting through EM, failover is occuring fine.I'm just wondering why is this happening only with dsn. If anybody could help me, that would be great. Thanks in advance, Preethi.