Emailed resolution link can't close call

I have managed to somehow break my user self-close request system.

When a request status is changed to 'resolved' the requester receives an email with the following content.

Your Request [ID:$RequestId] has been resolved.
Title : $Title
Description : $Description
Resolution is : $Resolution
Click here to Close Request (this uses close request link from content variables)
$RequestAge
If not satisfied, reply to this mail to re-open the Request

This is all ok so far and you can click on the closerequest link which will open a web page showing the call detail with a "Close Request" button. However, this button is
not working and simply reloads the page dropping the ?woID=xx&KEY=xxxxxxxxx
off the end of the link.

The call remains with a status of resolved, and I have checked that all the mandatory items to close a request have been actioned. Also I removed all
mandatory items and it still won't close the call.

Any ideas my fellow SDP users?

Kind regards,

Dean