Always wondered what causes the crash.
If you are using the PES Editor, stay clear of moving players to where they aren't meant to be ie Edited Nationals in club teams. Generally, I would only do things that in game PES allows. I fear that importing teams over licensed ones may upset the game too. I hope my hunch is incorrect, as it is vital for all OF makers to be able to use all teams in the game. The safest ML is with an OF that is untouched. Sad but true