I finally managed to rebuild the import table and get rid of all the protection's code. I was able to do it by manually building an IAT from the relative calls and replacing them with normal "FF 15" calls. I also resolved the 18 emulated functions. Thank you again to everybody who helped me here.

The strange thing is now that I have one real and one emulated "SetLastError" API call. Does anybody know if there is an alternative name for this API? I had two more double entries, but it turned out that the same function was exported under two different names.

Now it's only optimizing the PE structure and playing hide and seek with the programmers so that I don't die after 10 seconds in the game while everything else works fine.