Sorry, this post is no longer needed, as I had found out what went wrong after I submitted it.
Unfortunately, I have not seen a way to delete a post, so I might as well describe the [solved] dilemma quickly.
I was trying to upgrade from PS 2.0 to 5.1, and just couldn't get ANY script to run, including [Install-WMF 5.1.ps1] despite typing:
many times, and Run as Administrator in PS. I kept getting the message "Execution of scripts is disabled on this PC".
Out of desperation, I rebooted my PC and then I was able to run [Install-WMF5.1.ps1] without the error message and succesfully upgraded to PS 5.1.