How far Waves plug-ins are backward compatible?

In some project (not my) there is an instance of plug-in called "Waves C4 Mono".
 
But Sonar/CbB can not find it, even after I have installed current "C4 Mono" (v10) and can add it into FX Bin (VST2 as well).
 
The project is old, from Sonar 7. I guess C4 used there is also old.
 
Any tips?

RSMCGUITAR
My guess would be load project in safe mode and replace the plug-in

The project can be loaded even in normal mode, that is not a problem. I have just thought there is some
known trick/behavior when/why some plug-ins can not be recognized.
 
PS. since there was no other replies, I have a feeling there is something special about that particular instance in that old Sonar. F.e. the plug-in was not available when the project was saved the last time, modern Sonars save them usual way but who knows what what the approach more then 10 years ago... I will dig deeper (the target is to open that project in another DAW... so I can manipulate the preset if needed).

Waves provide old installers back to Version 8 or 7 I think. It seems that each version is compatible for only so long. If you look at that area of Waves.com you’ll be able to find out for which versions of Windows each version of Waves is compatible.

Edit...

CbB matches plugins by CLSID#. 
So DX version and VST versions won't be identified as same plugin.
Waves stopped supporting DX after 5.97 and don't know if they ever had 64bit DX versions - CbB will only support 64bit DX plugins.
So you might be SOL - where you can use the new C4 Mono but one currently embedded in track is dead.
If find a way to decipher the preset settings let us know I have similar issues on a couple of old projects.
 
The info below is probably not relevant but I'm leaving it in case someone finds applicable to their situation.
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Chances are that the plugin failed to scan properly - I had that issue with a bunch of my Waves 10 plugins and it drove me crazy till I figured out what was going on.  You may be having the same issue.
If so here's how to fix it:
 
After verifying that that you have a license for the v10 version and have it installed (if it's not including in one of the Waves bundles you own).
https://www.waves.com/plugins/c4-multiband-compressor
 
Assuming that you don't want to do a complete VST Reset* (which should fix but takes longer) then with CbB there's a 2 step dance to fix this.
*Rescan All Plug-ins might work but think I tried it and it didn't.

• First go into the registry and delete the C4 Mono data from the VST scan database
  Here's what my Registry Keys are, yours may be different because your scan paths may be:
  Computer\HKEY_CURRENT_USER\Software\Cakewalk Music Software\Cakewalk\Cakewalk VST X64\Inventory\c:/Audio/VST64/has vst3 version/WaveShell1-VST 10.0_x64.dll*1145393485 C4 Mono
  
  Computer\HKEY_CURRENT_USER\Software\Cakewalk Music Software\Cakewalk\Cakewalk VST X64\Inventory\c:/program files/common files/VST3/WaveShell1-VST3 10.0_x64.vst3*104 C4 Mono
  
  If you compare the registry data for these with a working Waves plugin you'll see that the broken ones have maybe 10 lines of data where the working ones have over 50.
• Launch CbB, go to Custom/Preferences/VST Settings.
  For Scan options only have "Scan in Sandbox" checked.
  and then click on Scan

For some reason in CbB some plugins only partially scan but aren't marked as bad, so "Rescan Failed Plug-ins" doesn't fix them because as far as CbB knows they're good to go and so on every subsequent scan they are skipped.
While this fix works if you have a lot of mis-scanned plugins it might be quicker to do a reset then rescan.
 
Hope this helps.
...Steven