Hi reck,
I was actually writing in reply to the topic starter's question.
Well, seeing how it's to do with Steam and their updating of the game, perhaps their customer service can help you with that. Vstep doesn't have direct influence over them, I'm afraid. Sorry, I can't answer your question, but I'm sure the people at Steam can, since they apply the updates.
Edit - I saw the bit about the previously installed demo. Perhaps your pc still holds some leftover files or registration from that.
I haven't used the demo so not sure if it has the unregister.exe tool, but if it does and you can't manually clean any and all leftovers from the demo.. installing that again and unregistering it with that, and then unintalling it again, might clean the rest. Once that is all gone, there's no reason for the newly installed SSE full version to find anything demo related anymore. If that's still not it, I reckon that the Steam people could still have a better answer.
Sorry, I'm not expert on this matter. But if it indeed is a conflict with the old demo install, then cleaning that up 100% should fix it.. keyword = should.
Regards,
Fred