I just had the same Problem. With the new Viking COnquest released i thought about getting back to M&B. God thing i didn't buy the Vikings DLC key yet.
I had a bad harddrive in my gaming rig a few years ago and did not reinstall warband since that. I was lucky to get the hdd working again long enough to retrieve my key. I also found an old e-mail with the receipt, so i could confirm it was the right key. So after spending a few hours of search and downloading the latest patch, i came to the fristrating message "Activation denied!"
On the website http:// wact.taleworlds.com/manual.php it says "Activation for this Serial Number has been denied."
How can that happen? It is definitely a legit key whoch i bought in 2012 and i only once installed it on the harddrive which is now broken (glad to be able to retrieve it still).
I want to use it on my newer Asus notebook now (i don't have a desktop computer any more after it broke down).
Please help me!