I was getting the following error every 4 minutes on the same sql server:
SSPI handshake failed with error code 0x8009030c, state 14 while establishing a connection with integrated security; the connection has been closed. Reason: AcceptSecurityContext failed. The Windows error code indicates the cause of failure. The logon attempt failed [CLIENT: ipAddress here]
All the googling I do points towards being unable to connect when running something, but that's not quite my problem...
The errors were coming from the same ip address every time, which I tracked down to one of our developers. They have permission to log onto that server, and had been successfully running queries on it earlier, through sql server management studio.
We looked at what they had running, and decided to shut down one application at a time until the errors stopped. We did Visual Studio first, and got another error soon after. Then we closed all instances of sql server management studio, and the errors stopped.
Why was SSMS repeatedly (every 3-4 minutes) trying to connect to this server, and why would it have been failing, when all queries were run with a valid login? Is there a way to prevent this happening in future?