you might try holding CTRL and SHIFT while Vegas is booting. It may be that something was corrupted. You might need to do a reinstall.
Upgrading to latest version (per Ralph's suggestion) might be a good one.
Douglas Spotted Eagle
Certified Sony Vegas Trainer
Re: Error occurred starting vegas pro by Nigel O'Neill on Mar 28, 2011 at 12:28:56 pm
You might want to do as Douglas suggested, and obtain the latest version for SVP 9 from Sony directly. Some forums suggest that the error you are seeing is the result of downloading a compromised version of Vegas from a BitTorrent site or similar. You should always get your updates from Sony directly.