Error calling saved object properties to script from workflow

Background:  I have a workflow that triggers on the modification of an attribute on a group (it contains who owns the group).  The groups in question provide access to servers so we need to keep the owners of the computers updated with what the group owner is. The groups are named adm-<servername>.     

I can get the workflow to trigger no problem but in order to trim off the adm-, i need to use a script as there is no workflow function i can find to trim the first 4 characters off a field so i can search against it.  Below is my script call but when it tries, i get Exception calling "SavedObjectProperties" with "1" argument(s): "The given key was not present in the dictionary.". 

$groupfound = $workflow.SavedObjectProperties("Save object properties").get("cn")
return $groupfound

The "save object properties" is just a default control pointing to the Workflow Target.  The CN is on the listed properties, i can see in the history that it is saving the proper object but not passing to the script.

I've also tried 

$workflow.ActivityTarget("Workflow to update computer sponsor")

no luck with either.