I am having the same problem. Was building in the game last night and tried to log in today and got the same error message "System cannot find file specified". I uninstalled all my mods awhile ago, long before this issue popped up. I tried to run a repair, but the repair just kept starting over when it finished so I cancelled it and restarted my computer to see if that helped. Still getting the error message and no option to try and repair again.
Update: The repair option came back and finally ran all the way through. I'm back in my game. Just in case it works for someone else.
