Well some times after possessing a familiar when your main char is attacked or when you return to the master, will fort and reflex go to -1 and skills also go to 0 or negative.

Solves with a relog, happened twice.

I think that's only a client side issue. All of your ability scores appear as 8's with the appropriate "-1" bonuses. They actually are still valid, they just don't get refreshed or something when you check the character sheet of a familiar (or a summon!) and then try checking your own character sheet. It happens all the time on the DM client. There you have to check someone else's sheet before you can go back and check the one you intended to look at. :(