Today on my Win 7 (VM install guest on Zenwalk Linux) VS 2012 RC expired. Hence i had to uninstall it. Unfortunately after it uninstalled, it did not clean up all the paths and links and corrected the changed paths of some too, in this case devenv command path (Beta build yea!). Though i restarted the VM twice, still the problem persisted. Hence i could not launch VS 2010 from Start -> Run or even from command prompt.
After googling for a while, i did end up with nothing apparently. So searching to fix this issue had to fiddle with the stupid windows registry.
So if you also face the same issue, here is the path for it:
Short and Hope it helps.