For some unexplained reason I see that a log file called amAuthJDBC, located in:
It's not the Sun One application server, but Access Manager that creates the log files in that location. Access Manager is an application that runs on Sun One app. server and it's used for authentication and such. I guess that the missing log it's for jdbc authentication.
If you feel that there is a problem with your AM server, you can go to http://your-appserver/amconsole
and see if you can figure out what's wrong.
I suggest you also to post your problem in Sun forums
(you need to register first), where you can find more specific help.