You downloaded the repo file into the yum repos dir, as it says to in the link you posted, right? You'd get an error like that when it's not found in the repos you have.
It may be simply that that version isn't listed currently. It's been awhile since I've used yum, but I'm pretty sure you can tab complete in it, so type like:
yum install Virtual<TAB>
Hit the tab button a few times, see what versions pop-up, install one of them (preferably latest). The version has to currently exist in the repos and it and it may have been updated.