Me again: I found out, that the error only occurs, when the bug-catcher I inserted is on the screen when a wild pokemon battle starts. After the fight I become him. I'm becoming the sprite of the bug catcher trainer, but keeping my things and pokemon. What did I wrong. Thats my Trainer Script:
trainerbattle 0x0 0x267 0x0 0x88017E1 0x88017F8
msgbox 0x8801811 MSG_NORMAL '"Hi"
It sounds like your sprite has the movement type 'Look Down'. Change it from that to 'No Movement'.