Don't know if you've installed it before but if you have, this (from this FAQ p.9) might apply: "Older versions of Vegas Pro [and Movie Studio] than 14.0 are licensed under a system (as previously used by Sony) which permits use on multiple computers by one user; after an unspecified number of installations on different or updated PCs you may need to contact support to reset your "installation count"."

And if you haven't, try and report to/contact support as advised anyway.