Refuses To Accept Selected Program To "Open With"

I'm having trouble assigning the default program to open certain files on my 64-bit 7 Home Premium machine. I previously had a program called Vesta which I used, and that was fine. The path was something like C:Program Files (x86)VESTAvesta.exe Then when I discovered there was a 64-bit version of Vesta available, I removed my old version and replaced it with the 64-bit version, now sitting in C:Program FilesVESTAvesta.exe

Now I'm trying to reset my .cif files to open with the new Vesta. Not surprisingly, vesta.exe has disappeared from the list of available programs to "Open With", because it no longer exists at the original path. But when I browse to the new vesta.exe in Program Files and select it, nothing happens - it just completely ignores my selection, with no message. I can Browse and select any other .exe program as normal, but there is no way I can assign Vesta as the default program. So, it must have something to do with the fact that the new vesta.exe has the same name as the old one, but a different path.

It seems like I somehow need to reset a hidden "Open With" app path list that Windows is keeping somewhere. Does anyone know how I could get at such a list - is it in the registry maybe? (At the same time it would be nice to remove all the random .exe's I added to the list while I was experimenting...)