Welcome to the forum.
When I saw the title, I was thinking something else. Reading it, I see that you are talking about problems with VST's that should work with PrPro.
Now, I have to admit that I'm not on a 64-bit OS, so this is pure speculation. The BassManagerPrem.dll works fine, and is recognized in my version of PrPro, on a 32-bit OS. Based on that, my first inclination would be that it is 32-bit, and is not being seen, even though PrPro is still a 32-bit program. Remember, that is but a guess, and even I see holes in it.
I have tons of VST's, and there are three behaviors:
1.) PrPro (and Audition, AE and some other programs) sees them, load them and can use them fine.
2.) PrPro sees them, loads them, cannot use them and the very first time, issues an error message to that effect - never to be seen again.
3.) PrPro crashes on some of these. Luckily, I've never had any that caused this behavior.
Because PrPro surveys one's system for installed VST's, and attempts to load and use all, the biggest task is usually to hide the #3 type VST's FROM it. I'd first look closely at the installation instructions, just to make sure that the exact Paths were adhered to. Since PrPro is still 32-bit, it should work with these.
I hope that someone else has better advice for you, and also experience with a 64-bit OS and PrPro - I am at a loss here.
I put my vst dlls into C:\Program Files\Adobe\Adobe Premiere Pro CS4\Plug-ins\en_US\VSTPlugins folder
and it works
Well, I looked into the folder you mentioned and found the CS4 installed VST pluggins. If you look there, you'll see that each of them has a number at the end of the filename. Either a 1,2, or 6. This must be for, mono, stereo, or 5.1 audio.
Hmmm...What if I rename BassManagerPrem.dll to BassManagerPrem6.dll, it is a 5.1 channel pluggin.
Voila....Premiere Pro CS4 now sees it, and it works fine. It doesn't matter if it's in the folder you mentioned, or in the " C:\Program Files (x86)\Adobe\Common\Plug-ins\CS4\MediaCore " folder. Either way works fine.
So far so good, next I tried the free VST pluggins mentioned on the Adobe website from MDA (Maxim Digital Audio).
What do you think happened?.......Nome of them were recognized.
I notice there were no spaces in the filenames for the adobe installed pluggins, so I renamed them all without spaces.
The only one of the 30 pluggins that were recognized was "mda RePsycho!.dll", that is, after it was renamed to mdaRePsycho!.dll" without the space.
Premiere didn't care if it had a number after the filename or not.
What the hell is going on?
It would be nice if Adobe would mention the naming requirements to get these to work so people wouldn't have to blindly experiment!!!
Why aren't any of the other MDA pluggins working?
Only 1 out of 30!
Does that sound right?