Although we've purchased subscription upgrades annually for years, one of our users prefers Autocad 2008, and uses it regularly. This morning he got a popup that he only has 14 days to activate. When he tried to activate, he got a message that his serial number was invalid. I found an old registration info file on his hard drive that showed a request code, but no activation code.
Subscription allows you to only run the current release and three versions back. Thus, your 2008 lease has officially expired. You may be able to file for an exception though, but a new serial number will have to be issued to you and it will only be good for 13 months. That's probably why your 2008 is expiring now because the time period from last activation exception is up.