meh
I think V-Vocal is 32-bit....looks like you have a 64-bit machine.  I've gotten it to work on my 64-bit machine by doing the 32-bit installation.

V-Vocal is 64bit and does not require 32bit SONAR to be installed on 64bit OS. Although there is a 32bit version too.

Can you select V-Vocal on any other clip or just this one?
 
If not I am betting one of 2 things happened:
1) The likeliest condition is the registry associations with the menu and V-Vocal got busted. Have you run any system/registry cleaners? You can try running the advanced SONAR installer again, un-check everything but V-Vocal. 
2) There's something up with DirectX dependencies. Installed any other applications lately? 
P.S. I noticed 2GB for system RAM in your signature. I would highly recommend upgrading to at least 4GB when using V-Vocal.

Maybe it's some type of permissions/registry issue.   Have you tried using the Windows "Run as Admin" option with the SONAR exectuable?
 
You could also try opening Preferences > VST, add the path where the cronus.dll is located, then rescan.
 

stevec
 
You could also try opening Preferences > VST, add the path where the cronus.dll is located, then rescan.
 

It is not a VST. That is not going to help.

Hmm good points here....

I use CCleaner on regular basic, maybe some regisration entry has been removed ? hmm.

Better reinstall, hopefully it will work then ;-)

Soundblend
Hmm good points here....

I use CCleaner on regular basic, maybe some regisration entry has been removed ? hmm.

Better reinstall, hopefully it will work then ;-)

FWIW, if you do choose to run CCleaner, just make a backup first. That way you can roll back if something does get screwed up. 

You can also manually register the files using a command prompt or the Run command

scook

stevec
 
You could also try opening Preferences > VST, add the path where the cronus.dll is located, then rescan.
 

It is not a VST. That is not going to help.

I know... but I could swear I remember a few people resolving VVocal issues by doing this.    Either that, or memory's not very clear.   Nah, that can't be it.   

stevec
You can also manually register the files using a command prompt or the Run command

It's likely still registered, the Menu pointers probably got hosed.

Seth Kellogg [Cakewalk]

stevec
You can also manually register the files using a command prompt or the Run command

It's likely still registered, the Menu pointers probably got hosed.

Oohhh...  Gotcha.   VVocal reinstall to proceed in 5, 4, 3, 2...