Just had this happen to me.
3rd Season in. Went to save the game and it only took about 3 secs, then the game locked up. Rebooted the Xbox and stuck FM2006 back in and tried to reload my save and got the 'game cannot be loaded' message. Career over
Think I'm going to run 2 saves from now on, one for the monthly autosaves and one for when I finish playing for the session. Hopefully if one dies i'll have a backup.
Very annoying though and it sounds like a genuine problem from the amount of people who have encountered it.