Problem using Powershell in the pre and post backup commands

I am running Acronis 2014 on a Windows 8.1 system. I also use that system to host Hyper-V computers. I have created a PowerShell script that will shutdown all of the running hyper-v machines and also shutdown hyper-v's lock on the disk. I have tried calling the PowerShell script from a batch file as well as entering it directly in the pre-backup command. Acronis runs something, because I can see a command window flash in the background, but it always seems to think it works, and it never actually executes the PowerShell script. For reference I attached is the PowerShell script , which works fine if run from the command line or run from the PowerShell ISE.

Any advice is much appreciated.