Update - It is safe to download now. See this thread http://steamcommunity.com/games/310560/announcements/detail/141082177881651526
Update - We've got to the bottom of the problem, just checking how different versions of the game will behave. Info/patch notes to follow
If you receive an update for DiRT Rally today please do not download it. If your Steam auto updates then please don't run it.
Look's like we've hit our first rock in the road and you could potentially lose your save game.
We'll update you later on our progress.