Fatal Error When Editing UserGroups

[bshutter]

Fatal error: Using $this when not in object context in C:\xampp\htdocs\forums\admincp\usergroup.php(337) : eval()'d code on line 1

[Marco van Herwaarden]

This is caused by an error in a plugin.

[bshutter]

Roger. How do i go about fixing this error?

Edit/ what plugin caused this