Fatal error: Cannot override final method assign_plugin::is_enabled() in Unknown on line 0

Hi all,

I am getting this error. All my assignments have been upgraded as far a I know.

When I create a new assignment, it all works but the message about "This activity is based on an older assignment module." appears still. I have disabled the old Assignment module.

When I click the link to "view the assignment upgrade tool" I get the error message Fatal error: Cannot override final method assign_plugin::is_enabled() in Unknown on line 0

Any help would be much appreciated.

Regards,

Richard