Return_key_not_found

It means you shouldn't use registry cleaners. Windows 7 does a much better job of maintaining itself than any previous Windows OS, and the past 3 or 4 did a pretty good job at it already. It sounds like the program deleted a registry key it wasn't supposed to.

Most registry cleaners backup the registry before they apply changes. Launch your program and see if it has the option to restore the orig. registry.. If not, look for a Win7 system restore point prior to the installation.

There's many opinions here on using these kind of tools, you'll have to make your own decision. Luck with it.