I have a problem with one of our SQL 2005 SP2 servers.
From time to time the performance decreases gradually until and all queries from client software halt in time out.
In the SQL log file shows something strange:
"Error 18456, Severity: 14, State:16
Login failed for user 'sa'.[Client: xxx.xxx.xxx.xxx] - most of the times is the IP of the server itself"
I must add that clients software authenticates with 'sa' user from the software itself so is not the case of misspelling the password.
I have used "perfmon - SQLServer:SQL Errors[Info Errors]\Errors/Sec" and I've found constant info errors even if no transactions are tacking place.
The server is a central cashier server. The client software authenticates through user 'sa' and the sql service is running under an domain account. The server uses bulk import&bulk export for some clients who run SQL Express and tcp with others.
The client and the server are in the same location so network connectivity is ruled out. The load on the server is minimal.