Just to let you know.
For a temp fix you need to edit include/class.staff.php
Find the following code:
function appendMySignature(){
return ($this->signature && $this->udata)?true;
}
Replace it with this:
function appendMySignature(){
return $this->signature?true;
}
Now you should be able to change the Signiture file for each member of staff.
Thanks to Peter the developer for the answer to this issue.