Invalid argument supplied for foreach()

I tried this on a test site and it worked great. However on live sites it’s a different story – plugin no work:

Warning	Invalid argument supplied for foreach()	1	wp-content/plugins/plugin-groups/classes/class-settings.php:129	Plugin_Groups_Settings->is_group()
Plugin: plugin-groups

Warning	Invalid argument supplied for foreach()	1	wp-content/plugins/plugin-groups/classes/class-settings.php:152	Plugin_Groups_Settings->bulk_actions()
Plugin: plugin-groups