'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 and ser2 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. Can anybody help me

error : 18452 in clustering; very urgent
Ravi Shanmugam
The error will be raised when SQL authentication is tried using an NT login account and it seems like the system is not able to find the login account. Make sure you are using the same account to connect after failover.
.NetAvoider
You can get this particular error in a number of scenarios -- the common scenario is when one attempts SQL authentication using an NT login account. If the system is unable to find the login account it will raise this error. It is not clear the scenario behind this error.