Hey there! I don't work for Lockitron, but I'll help as best I can.
Sounds like there's a few things going on, least of which is pending Firmware Updates.
When the Lockitron was initially registered, the serial number would have been bound to that account, meaning it can't be registered again. The only way to register it again is to remove it from an account.
If you're using the same e-mail that you initially registered with, you might have to unregister the other entry.
If you're using a different e-mail, see if you can reset your password on the original account.
Failing all that, email@example.com can help remove it for you (with proof of ownership).
Once you do get it to clear, then you can go into the app, bring up the menu, and choose "Support". There should be an option to "Clear WiFi Settings", and this will start a BlinkUp sequence that "resets" the Lockitron.
After you successfully clear it, you should be able to register and proceed.
Be aware that once you get it linked, it'll spend some time to update both Firmware and Bluetooth chips until it's back up to a running state. You can check on the status through the app, or through the Lockitron.com dashboard, under Settings.
If it gets stuck for a long period of time, you can also use the Web dashboard to push them through again. You may need a quick battery pull to restart the firmware process if this happens. If you do have to push manually, I believe it's AVR Firmware first, then Bluetooth.