I just had a horrible shock! I loaded my save in Fable 2 to discover all of my hard-earned experience had been reset to ZERO.

After a quick Google I've discovered the reason; If you play Co-Op with someone in the Childhood Prologue the glitch occurs. There is no way to regain the xp lost without cheating, and I think Renown is affected too.

More information can be found on the Lionhead website, I really hope it doesn't happen to you to, it's really affected my enthusiasm for this game :/