I am at wits end-still getting error messages

Hello to all and I hope that you can be of help to me. For the past couple of weeks I have been receiving error messages on executables that I download manually such as any Windows Updates, Visual Basic, Windows Installer, actually anything to do with Microsoft updates/patches/hotfixes and the like including a couple of other general programs.

The error messages are as follows and I was able to download everything just fine until just out of the blue I started to receive either one or both of the error messages:

"Extraction Failed. Cannot Find Window Class"

"The installation program appears to be damaged or corrupted. Contact the vendor of this application."

The RPC is available. I have run SFC. I have run ScanDisk and Defrag. Nothing has worked.

I have run Dial-A-Fix plus the Repair Permissions and Repair Associations. I have checked for Spyware and Viruses. I have reset all File Extensions and File Associations.

Some executables open like CCleaner and Dial-A-Fix, some don't.

Nothing I have tried to do has fixed the problem.

However, all the executables that are on the computer, such as Word, Regedit, ScanDisk, Degrag are working just fine.

It is just when I download something like Visual Basic Update or a Windows Update manually that I receive these error messages. The program downloads just doesn't open. And it doesn't matter if I save it to my computer or run from the current location-same error messages.

Again, this is just a recent occurence. Two weeks ago everything was working just fine and no error messages.

I hope you can be of help. I am at wits end!! It seems to me that I need to Associate the .exe File Association with the applicable Window Class but I don't know how to do that and I don't know how it got messed up in the first place. There must be a registry error somewhere.

Thank you!

Richard