I found the same error when trying to update the user.
It appears that if you do no have the "Delete fetched message(s)" box ticked the SQL it generates is not correct.
The column mail_delete is set as blank instead of a 0/1 which MySQL will not allow. For the moment I just make sure I have ticked that box.
Perhaps the developers could look into sorting this issue!
Note: Even if you have not enabled that section of the form it still effects the SQL.
Alex