Can I assume it's OK to: (1) install Vegas 6 with Vegas 5 still on board, and (2) later uninstall Vegas 5 including registry links, DLLs and the program file folders for Vegas 5 and Vegas 5 setup, without disrupting Vegas 6?
You can install Vegas 6 on any system running earlier versions, they will coexist with no trouble. One of my laptops is running 3,4,5, and 6 without a hitch
I've had this problem a couple of times with SoFo/Sony programs as recently as Sound Forge 8. Install SF8 and everything seems fine. Uninstall SF7 and SF8 no longer has certain features like Wave Hammer. Migration Tools in the Sony Program Folder didn't fix the problem either. Simple solution is to uninstall SF8 and reinstall it. Wave Hammer is registered again and everything works fine.
I haven't uninstalled V5 yet so I don't know if the problem will recur but I expect it will.