Any attempts to adjust the sound volume on my system gives me an unexpected error message. I enable the log and got the following entry.

5/7/2015 11:50:47 AM 411 unexpected error in action: Sound.SetVol
System.IO.FileNotFoundException: Could not load file or assembly 'CoreAudioApi, Version=2.0.0.0, Culture=neutral, PublicKeyToken=f66bdc7305ed7bf3' or one of its dependencies. The system cannot find the file specified.
File name: 'CoreAudioApi, Version=2.0.0.0, Culture=neutral, PublicKeyToken=f66bdc7305ed7bf3'
   at eval_᜚.eval_ᜀ(String A_0, String A_1)
   at eval_d.eval_ᜃ(macroElement A_0, List`1 A_1, Int32 A_2)
   at eval_d.eval_ᜂ(macroElement A_0, List`1 A_1, Int32 A_2)

This is an older Dell machine running Vista. I don't see anywhere on my machine where a CoreAudioAPI dll  file exists. any ideas?

Can you double-check the dlls folder of your VC installation? It should be there.

If not, maybe try to reinstall VC.

Already looked and it's not there. Also an uninstall/reinstall was one if the first things I did when I saw it was missing.

Hm. What version are you using?

I have now downloaded fresh versions 2.145 and also 2.142 from the VC website and installed each of them in fresh folders. The CoreAudioAPI dll is there in both installations in the dlls folder.

I'm on a Windows 7 machine, not Vista. Not sure if that could be the culprit or not.

Anyone else here on a Vista machine who could test this? I don't think we have any Vista machines in the house anymore.

@OKGreyBeard -- If you tried to reinstall VC using an installer exe you'd previously downloaded, perhaps you can try downloading it again in case somehow your installer file got corrupted. Or if you have virus protection on your computer, who knows, maybe it didn't like that dll?

Did you enabled the Audio endpoint plugin in VC? I'm not sure it has to do with that 

Found the issue.... Anyone want to recommend a replacement for AVAST? (which used to be a really nice unbloated program)

I have disliked AVAST for a long time now.  It is not just bloated but terrible for false positives.

I have always liked ESET NOD32 and it has never interfered with any legitimate programs I have used AFAIK.

It is a bit expensive but they have a 30 day trial.

If you want free free, AVG is not so bad but I prefer NOD32.

Of course, that's just one guy's opinion.  I'm sure you'll find plenty of other opinions out there.