I see many people have had this problem and a lot have been solved by applying correct permissions. In my case this has been working for about 5 years straight with no issues and permissions have not changed at all to my knowledge.
What are some other log files I can look at to locate a problem?
The only thing I have done thus far is restart the server and that has not resolved it.
I have 1 primary site and everything is on 1 box, SQL and primary site server are the same server.