Mountain Ghost - Had the EXACT same issue as you...
Called B&H prior to purchase to see if I could upgrade from Vegas 5 (full version) - they said yes.
Called again when I received the package and the sticker on the front said you needed v6 or v7 and they said install it anyway because Sony probably ran out of room when printing and didn't include v5. Got the exact same error as you when I tried to install.
B&H told me I could return the software and get a refund for the software and shipping in both directions - so far I've received the refund for the software but have to call again to have them keep their word and refund the shipping also.