I was trying out a demo of Shredder, and it wouldn't read the pgns I had downloaded from Chess.com of Chess960 games. I contacted their help and support, and they said Shredder expects a different FEN string for the pgn file. Instead of " nbrkbqrn/pppppppp/8/8/8/8/PPPPPPPP/NBRKBQRN w KQkq - 0 1" it expects " nbrkbqrn/pppppppp/8/8/8/8/PPPPPPPP/NBRKBQRN w CGcg - 0 1." That is, the bit for showing that castling is legal indicates the file of the rook(s) that it is legal to castle with. I noticed that ChessBase also accepts this format, where it doesn't accept the KQkq format. I don't know if this is universal, but that is two popular programs using this format. Would it be possible to have the Chess.com pgns use this format also (for Chess960 games)? Or do I need to write a python program to convert all my pgns?