Depends if it happened only once or if it happens every time you turn the game on.
The engine sometimes hangs for no apparent reason and just throws a random error like this. It happens randomly, very infrequently and you can just turn the game back on and it should work normaly.
If it happens every time you turn the game on, then something went wrong. I never got this error and I have no idea what could be causing this.
Try deleting the "Settings" file in the "Data" folder. See if that helps.