I found this thread after getting the VT-x disabled message when I started Parallels today. It worked yesterday (after first installing) without a message, as others have stated. I've tried the various sleep/pulling-the-plug etc tricks, without success.
There's a lot of talk about whether VT-x is enabled on different firmware/serial combinations. But isn't it overlooking the elephant in the room? Couldn't it simply be a bug, sorry a "feature", with Parallels that's causing it to be disabled, or reported as disabled?
Why did it work first time but give an error after the Mac is rebooted? I'd say there's two possible choices:
1. It didn't detect the setting was disabled the first time it ran.
2. It changed something that didn't manifest until after a reboot.
Does Parallels install/change anything that could related to the firmware settings?
Has anyone tried restoring a Mini (does this only happen to Minis?) from a backup or to a clean install... Then run the vtx-check pre and post installing Parallels to see what happens (can you restore the firmware too? - I don't know.)
Just a couple of thoughts.
P.S. Nice work Parallels people.