guest script error - powershell script type is not valid for OS null

I am using the guest script manager to run Powershell script on a newly cloned Windows VM. In my master workflow I call several vm workflows (upgrade tools, shutdown vm, relocate DS, etc.) which use: In Attribute called newVM  of type VC:VirtualMachine. I added a new sub-workflow to run the Run Script in VM guest. I did as the other sub workflows and bound the vm VC:VirtualMachine Parameter to the newVM. Also bounded the parameters for password and username. I can run the sub-workflow Run Script in VM guest by itself with no issues. However, when I run the master workflow which has the sub-workflow embedded, I get this error: powershell script type is not valid for OS null