I've notice many users have problems with using Eventide plugins when I went looking for answers to the same issue. I found no help available in solving this issue. So I solved it myself and thought I'd share the answer that I came up with. It's really quite simple, honest:
A. DOESN'T WORK:
C:\Program\Files\Common\VSTT2\Eventide
*B. WORKS:
C:\Program\Files\Common\VSTT2
*B The same goes for all variants; install it into the Main Folder..
I hope this works for you all as well. I'm seriously loving Studio One Pro having just moved across from Cubase Pro. I've not found anything I've missed, except colored Faders and it could be done better.