Hi,
core_error/cannotfindgroup is in use in mod/forum/lib.php and mod/data/lib.php and mod/wiki/lib.php
In reply to Shamim Rezaie
Re: greylisted string in use: core_error/cannotfindgroup
per David Mudrák,
Good catch Shamim! I just removed that string from the greylist. Thanks for the report!