I've been trying to submit a Guitar Pro file, it's a .gp5-file, but whenever I try to submit it I just get to a page saying "Wrong file format!". What can be wrong with it, I have also changed it to all other sorts of supported Guitar Pro file formats but I still can't submit anything. The first Guitar Pro file I tried to submit worked perfectly but since then I had this problem with several different files. Does anyone have an idea how to solve that problem?