What version of Reaper are you using? Previous versions had a problem with Waves VST's due to an incompatability with the Waves' Waveshell. That supposedly was fixed for version 1.869 and after.
DX versions of the Waves plugs should work fine in versions prior to that. The VST versions were the only problem. If you are still having issues, and it's a newer version, make a bug report at the reaper forums on their site.
I dealt with something like this in Cubase the other day… For me...It was a bad plugin... <O</O Check it out my man…It could be a number of things -Do you have the latest version of Reaper? Try to update if not.<O</O -Update your plugins.<O</O -Do you need a dongle for any of your Waves Plugins? Make sure you have one…<O</O If you have bootleg Waves Plugins…then that’s probably the reason they don’t work lol.<O</O -Do you have old instances of Waves plugins on your computer...if you do, delete the old versions or, if you update, delete the old versions first, and then install the new versions.<O</O -Another thing you could try is download a program called CC Cleaner. <O</O It'll clear out any old temp files on your computer, and clean up your registry. Old or conflicting instances of old programs can mess with your registry.<O</O The best thing about this program is that it’s free! Gotta luv that.<O></O> Finally, maybe you have fragmented copies of files or hard drive clusters on your computer. A defragmentation program like Diskeeper might help. Windows also comes with a defragmenter program pre loaded.<O</O <O</O
You can find it by going to the Start Menu>Accessories>System Tools>Disk Defragmenter.<O</O
There is a setting in Reaper in the Preferences/Settings... you can turn off "acquire VST plugin-names on load" or something like that. I forget what it's called. But turning that off can prevent Reaper from crashing on VST scans sometimes.
Of all the VST hosts I've seen, Reaper is the most tempermental when it comes to VST plugins compatibility. I hope someday they get the kinks worked out of it.