C5 - "The plug-in (...) could not be found for Insert..."

Hello to you all.
I have a horrid issue with reloading my VSTs after reinstalling Cubase 5 on my newer Windows 10 64bit laptop.

I know for a fact that these plugins can work in Cubase 5, I have done it before and I found previous screenshots of it working, so I would love to get 'em back.
I placed and poured a bunch of older VSTs (from Cubase SX3) below the program folder in Cubase\VSTPlugins, but some of them will not load.

At first program launch, it tells me that RoomWorks, Reverb A, Magneto, Nuendo Compressor, SurroundDither, MultibandCompressorand UV22HR, “doesn’t work with this host” and for each of these, that _“File SYNSOACC.DLL could not be located in the Windows system folders”_and/or “File SYNSCOACC.DLL does not have the expected interface”.

Another strange thing about this, is that most other of these ‘old-ins’ do work perfectly. For example Reverb B, Q, a.o. Then you would think the rest would work also.
And when I load my mixes, the used, non-working plugins are displayed under Inserts like “!!! Reverb A !!!” i.e.

Any help is deeply appcreciated!

Excuse me for bumping this one to hear if there’s any clues.

Noone has any clue about these SX3 VSTs? It really used to work in Cubase 5, don’t get why they don’t do now.