Please go to the STEAM install folder of the software, normally it is located on C:\Program Files (x86)\Steam\SteamApps\common\Magix_Software_Name
Look for the file .exe file and delete it.
Then go to the Protein Folder and locate the file Protein.dll, please delete this as well.
Go back to the STEAM library and right click on the entry for Vegas and select Properties.
Then go to Local Files and Verify the Integrity of Application Cache.
The install should rebuild itself and this problem should be resolved.