I experienced exactly the same on a 6.0 box (posted it here some weeks ago), it was a bug in a certain amavis version. Updated with the package from pagefault it will go away. There is another solution which is described in the old post.
But there is definitely a problem with the user panel user vacation/autreply/enable procmail panels. I have not dug into that but fiddling around with that will break amavis/spamassassin settings. Better you leave hands off that.