Hi! Finally, the problem is solved! Thanks to Michael and you other guys.
This is how I managed to get it to work: - I removed every path, and closed Reaper. - Opened Reaper again and just added C:\Program Files\Steinberg\Vstplugins - then I 'Re-scan' and closed Reaper. - opened it again and searched for VTM-M2, and yes now Reaper saw it. - then I added my other paths, i.e. C:\vstplugins\acustic, C:\Program Files (x86)\Steinberg\VstPlugins etc.
Conclusion: Seems like Reaper likes to scan all the 64 bit plugins first, close program, reopen, and then add 32-bit plugins etc.
NB: I had saved all my paths to a backup notepad txt-file and added all those paths in one go. That's not the way to do it obviously. So first add the 64-plugin path, close, reopen and then add the other paths, if you have any.
PS: nope I didn't had a 32-bit version of VTM-M2 installed (which I thought!)