strange, but let's find out which value causes this:
open /admincp/arcade.php
search for
Code:
print_description_row($ibforums->lang['acp_game_error1']);
and replace it with
Code:
print_description_row($ibforums->lang['acp_game_error1']."<br /><i>".$check_key."</i>");
(you will find this twice in the file, replace both)
Then try to edit the game again and tell me what the error-message says now