Unable to unlink a work task from a Service Contract after a creating a service invoice

We have Work Orders that were not supposed to be attached to a Service Contract.

I’ve reopened the Work Order and was able to remove the Service Contract from the WO, but I’m not abe to remove it from the work tasks.  I’m getting an error message:  

Is there another way to unlink the Work Task? The amounts should not be deducted from the Service Bank and should not appear on the Service Bank Report