I can not bit and turn my elderly alien sim into a vampire..

It's most probably due to the fact that it's an alien. You can't have hybrid Sims so Aliens can't be vampires as well.

Best is to try if it works on a normal Sim and if it does, I think that's the issue

If you're not opposed to mods, you can give the MC Command Center a try. That does allow alien/vampire hybrid but I'm not exactly sure how you get them with the mod.