Just brought Vegas Movie Studio Platinum went to register the the serial number and it said that the serial number has been registered to another email address.
See the standard Support advice here
Ask Support starts here
I did all of that and still getting the same result
Then you need to contact support as advised in this thread by a VEGAS team member.
A user-created tutorial here
OK, I dug through config files and registry entries and could not find a way to change the registered email address. What worked for me was uninstalling and reinstalling. On first startup I was able to change the email address to what I used to purchase the bundle.