I see you haven't had a reply to this yet... I seem to have a similar (maybe the same) problem -
I just treated myself to a copy of Waves L1 Ultramaximiser VST plugin (part of Waves 7.1, same as your GTR Solo).
As far as I can tell, it is installed correctly, and authorized on my iLok dongle.
However despite adding the path to the plugin in Reaper Preferences > Plugins > VST (it lives at C:\Program Files (x86)\Waves\Plug-Ins on my machine), L1 Ultramaximizer doesn't show up in the list of plugins.
When I clicked "Clear cache/re-scan", I get a dialog popping up 3 times during the scan saying "The program can't start because WavesLib 7.1.dll is missing from your computer. Try reinstalling the program to fix this problem"
The thing is, WavesLib 7.1.dll *is* present (it lives at C:\Program Files (x86)\Waves\Plug-Ins too). I tried reinstalling Waves (both using the Repair option on the installer, and completely uninstalling it and downloading again from scratch) but this didn't help.
Any suggestions? Having just paid $200 for L1 Ultramaximiser and $80 for an iLok dongle, needless to say I'm a little disappointed
Could the filename "WavesLib 7.1.dll" be confusing Reaper's search? (since it has a space and two dots in it?)
I am running Reaper 3.74 x64 on Windows 7 Ultimate 64 bit.