0.1 in error means .750 fielding percentage. You can check it during a game. That means he will drop 1 out every 4 balls he gets to.

A rating that bad usually (always?) means the guy played a little at the position but had no attempts.

Its better to play somebody else out of position. Someday I'd like to see that changed; the error rating should be consitant, especially for OFs.