After taking a look on it, I found out that the Battle system was bugged out by the SDK, and no the menu. But infact, it popped out a error in the menu script after loosing a battle. A guy from another site looked at the error, and said to me that the whol Window_Base script needed to be edited, and he didn't had the power to edit it.
Anyway, I removed the menu script, and Im searching for a new 8 Player menu system.
[RESOLVED]