What does this mean?!?  There are 3 copies of this file on my machine -
the one in "C:\program files\cakewalk\shared plugins" is version 14.0.1.199
the one in "C:\program files\pro53\bin" is version 10.0.1.184
the one in "C:\program files\cakewalk\shared dxi\audio simulation\dreamstation dxi2" is same version 10.0.1.184
 
How do I fix this?  If I just click OK, Sonar X1 opens up (apparently) normally.  What software do I "reinstall".

Are you running Sonar as administrator?

Well that was an experiment (running as admin) that I wished I hadn't done ... it unregistered several of my softsynths and effects.  I don't have hours to go fix that.

After quitting and then restarting the program in 'normal' mode, the same error is there.  And it 'seems' my plugins are now functional, i.e., registered.  [hope hope].

OK, here is how I fixed it in case anyone else has this problem, which just suddenly started occurring for no good reason.

I copied the dll with the most recent version to C:\windows\system32

there ya go

I downloaded the trial version, I'm currently running Sonar 8.53, and I'm getting the "not found, try reinstalling" message, but it appears to open and I can load an existing project, but that stuff bothers me to the extent that I want to uninstall and keep my good ole 8.53. And yes, every is run as administrator...
Why?!!
Btw, win7,64bit, quad i7, 16gb ram.

did you by any chance add an paths to the plug in manager?
 
(like a new path for 32 bit plugs, example c\programfiles(86)\cakewalk\32bitvstplugins)
I typically create a new folder for all my 32 bit plugs in the programfiles(86) directory.
but if I put in a stray path by mistake ive ended up with a similar warning.

Try the fix suggested by the OP. It should work.

When the program installed, it found all of my folders "from a previous version", maybe because I have 8.53?
what is this cwdxpx1.dll? It still loads, seems functional, and the copying of the dll as suggested can't be found. Perhaps because I'm running a 64 bit version?

The system32 directory is Window's backup plan for dll loading. If it can't find the find the object in the registry listed directory, it falls back to the current directory, and then system32.  
 
Try running regsrv on the dll from the directory you want it in - that should do the trick.