Copy of the game is out of sync

[:1]"Your copy of the game is out of sync. Try again later". I'm getting this message most of times I try to play co-op with my friend. I tried to play co-op with another person, but we both get this message just before we killed General in Renegade Escapada quest.It happened 4 times in a row in the same moment when we beating that General. I tried another quest(that argos chain) that worked fine in co-op mode and there were not any dissconnects or errors. But in Renegade quest it's happening all the time. Are there any tips on how to fix it?