The game freezes when attacking a unit!

Please help if you can... I borrowed 5 heroes from a friend... played for a while... then I bought the Gold Edition of all 3 parts... uninstalled version 1.0 and installed the new one... 1.6... of course, I kept the saves, I don't want to replay the campaigns... everything seems fine, but when I start a new mission, the game unexpectedly freezes... I restarted the game, and it freezes during the next battle... and this is at the beginning of the mission! Strange! Version 1.0 worked without problems... maybe the saves are just not compatible with the new version? Thanks in advance for your answers... I'm looking forward to them!