did you install the five updates(1.2.1.0~1.2.3.2)?
Are you trying to join people by disabling the filter?
In either case, incompatible map means that they're using a map that you don't have; you need to search for that map, download it and put it under "Documents\My Games\Company of Heroes\ww2\scenarios" or wait for a hosted game or host a game or use automatch to find a game.
Do you remember the name one of those maps?
I don't remember if they appear though.
