Try these steps. I had this happen before and this worked for me.

1. Cause the ''Invalid Value for Registry'' by attempting to run QTP test from QC.
2. Open Control Panel > Administrative Tools > Event Viewer > Windows Logs > System
3. Find the most recent instance of a DistributedCOM (DCOM) error that looks like the following (values may or may not be the same)

The launch and activation security descriptor for the COM Server application with APPID
{6128A57D-9219-41D6-8C0F-97E3AE0D4D81}
is invalid. It contains Access Control Entries with permissions that are invalid. The requested action was therefore not performed. This security permission can be corrected using the Component Services administrative tool.

4. Copy the APPID
5. Start > Run > Regedit
6. Select the very top item in the regedit tree (this will cause it to search the entire registry instead of starting from the currently selected item)
7. CTRL+F (or Edit > Find)
8. Paste in the APPID and start the search
9. Rename the AccessPermission and LaunchPermission keys to something else (example: AccessPermission_Old and LaunchPermission_Old)

That should do the trick!