I decided I had had enough. I uninstalled AP 5.12 and installed 5.10... Same problem.
So I decided to just nuke that as well and installed the exact same 32-bit 5.10 that I have on my XP machine. This one works, at long last.
Comment on Re: Unable to enable - trying to add repositories to PPM (ActivePerl 5.12)
I know this is old but I stumbled upon it so I figured some one else might.
I fixed the "Read only" Error by running a CMD as Administrator and running PPM. It opened the GUI and I was able to mark all packages for upgrade. I assume it will work the same for adding repos as well.