I’m sure there are some folks on this forum that could answer this question better than I could, but I’ll be glad to relate my experience and maybe that will help…
Before upgrading my FCP Studio, I was using FCP 5.1.4. (I had purchased 5.1, and the “.4” was an auto on-line upgrade.) When I wanted to upgrade to FCP6 (Studio 2), without knowing better, I bought the “Upgrade from Final Cut Pro or Production Suite”. The product number was MA887/A. Well, there’s the trouble… I technically I didn’t have “Production Suite” to begin with! So when I entered the serial #, it said it was Invalid.
Turns out what I actually needed was the “Upgrade from Final Cut Studio”, product number MA888/A. Bought it, and it took the serial number just fine, and upgraded with no problem.
One concern I have about your post is that you mentioned having FCP 4.5. I’m wondering if the trouble you are having is due to you not having the most recent version (FCP 5.1.4)???