Please be aware that subsonic is not currently compatible with Java 1.7.
Sindre is aware of the problem and hopefully it will be resolved on the next update.
So if you wish to continue using SS without problems tell the nice folks at Sun to go away for awhile
EDIT: For further info on the problem see viewtopic.php?f=2&t=9720&hilit=sun+java#p42249
(Thanks to hakko )
But the upshot is (I believe) that if java/SS finds a problem with something in the one of your tags it used to just go "tut tut!!"
and carry on as usual - now it throws up an error