Upgraded from what version to 2.9.1?
In the lib/ directory of a 2.9.1 code folder there is an upgrade.txt file that has a section
DEPRECATIONS:
Various previously deprecated functions have now been altered to throw DEBUG_DEVELOPER debugging notices and will be removed in a future release (target: 2.8), a summary follows:
In Misc:
* filter_text() -> format_text(), format_string()...
* httpsrequired() -> $PAGE->https_required()
* detect_munged_arguments() -> clean_param([...], PARAM_FILE)
* mygroupid() -> groups_get_all_groups()
You might have fallen victum to hyperjumping. :\
Do you have any *addon* plugin in the old system (the one you upgraded from) that related to 'mygroup' or groups?
'spirit of sharing', Ken