You must add it in the 'Front-End error messages' to have it works... Also, you can add something like 'hideaway_added' in the 'Front-end redirect message' and modify this line:
PHP Code:
eval(print_standard_redirect(''));
by
PHP Code:
eval(print_standard_redirect('hideaway_added'));
It's what I've done, it's working perfectly now, people can create groups/forums.