Please upgrade to 2.2 here.
The 2.0 and 2.1 branches are no longer being updated.
Error Code : Call to undefined method Gdn::Controller()*
A question was asked about this Plug In add On about this Error Code in the Dashboard..
Fatal error: Call to undefined method Gdn::Controller() in /path/to/html/network/plugins/ThankfulPeople/class.thankfulpeople.plugin.php on line 267
When will the question be addressed ?