Assignment error

Hi folks,

I have a IOMAD version (2.9) of Moodle installed, when I try to create an assignment I get the following message:- 

Error 500 Server

(1"/course/modedit.php?add=assign&type=&course=15582&section=1&return=0&sr=0".

I raI ran the debug mode and got the following message:- 

Fatal error: Class 'assign_feedback_offline' not found 

Would appreciate guidance on how to rectify this.

Kind regards,

Mark