I'm also having the same issue. I was able to contact SoftWrap to get my original purchase reference, but so far they have been unable to give me an actual license.
I can install GM 8 with a fresh install and activate the full version with this purchase reference with no problem... even on a new machine... but when I try to use this purchase reference for the GM Studio upgrade, I am told that it is not valid.
I contacted YYG support and this is what I was told:
Unfortunately we can not recover any GameMaker 7.0 or 8.0 licenses as these were supported by a completely separate company (Softwrap) who distribute and handle the licenses.
We do not have access to licensing information or account details.
Thank you for your enquiry.
YoYo Games Customer Support Technician"
I'm not sure what's going on here, but it doesn't seem like everyone is on the same page internally when it comes to this upgrade offer.
I suggest that everyone open a ticket and maybe even send out some tweets to get their attention so we can get some kind of official word on this.
Has ANYONE gotten this to work?