I'm somewhat stuck. We have a database server which was set up and configured by a third party. It's for a third party product so unfortunately we're stuck with the way they've configured it.
Their brilliant configuration includes using the sa account to make a number of connections. For about a week now we've had connection failures filling up all our event logs, two every ten seconds. I have managed to identify that it is the master database this login failure is for.
It's definitely the sa account accessing the master database. It is not an incorrect password (which is good, because we don't know the sa password - and neither does the vendor, it seems. Yay...) because we're getting error state 16 so I believe the sa account has some problems with the master DB.
It's connecting to everything else without problem - I can see the connections made to all other databases successfully. I have checked the sa account permissions and I really can't see anything wrong. I'm at the point of restoring the master database from a backup two weeks old and wanted to open this up to you awesome people out there in case any of you have come across this before and have any alternative suggestions...
Edit: Aaron kindly took a look as per his answer so I was going to post up a screen print, but I've been on stackoverflow mostly, and only recently come to the dba site...therefore I don't have 10 reputation yet, and can't post an image. However I've added it to stackoverflow so please check it out here.