Try inserting this or something similar) at the appropriate point in register.php ….
<?php if (!( 'completed-confirmation' == bp_get_current_signup_step() )) {
echo '<p><strong>There was an error - check below to correct any error and resubmit the form.</strong></p>';
}?>
Have deactivated an ancillary BP plugins, and deactivated and reactivated just Buddypress. No change, still receive “There was an error saving group details, please try again.”.