10.5.1 Server Locking The Administrator Out!!!

Hi All, I am having a few issues with my new 10.5.1 Server. Every day or two, it decides that it is going to lock the administrator account out, and also deny access to AFP and Samba users. I can only fix this by a restart. I have two weeks to figure out what is going on, before I have 500 users trying to log in, and if it decides to lock everyone out that will be great! Anyone experienced similar?