Most often when you have to execute some PowerShell scripts through the GPO and you end up with an error on execution saying that the Execution Policy does not allow you to run un-signed script.

So you would need to create a new GPO to set the Execution Policy. Create a new  GPO and edit it.

Goto Computer Configuration/ Policies/ Administrative Templates/ Windows Components/ Windows PowerShell

Double-click on Turn on Script Execution
Click on Enabled
Select Allow All Scripts

Move the GPO onto the respective OU, wait until the refresh or simple run gpupdate /force on the computers.