Nevermind, this specific problem seems to be solved. When giving the Function a bank handle that contains hacked adresses of further banks, blitz seems to dislike when a dll tries to write to those further banks. At least it could be solved when the bank points to itself, with some offset range.
Now I have other problems to solve (troubles with the bitmapinfoheader).
Now I have other problems to solve (troubles with the bitmapinfoheader).