I had MBAM registered for a while now, but I recently updated and all of a sudden, it said I wasn't registered. I tried registering again, but it said my serial was invalid! Any help please?

Please make sure that you are copying and pasting the ID and Key into the proper fields, and that you are not including the words 'ID' and 'Key'.

If you believe you are doing this correctly, then please uninstall Malwarebytes' Anti-Malware, restart your computer, run the utility at the following link, restart your computer again, and then reinstall Malwarebytes' Anti-Malware.
http://www.malwarebytes.org/mbam-clean.exe

You can download a fresh copy of Malwarebytes' Anti-Malware from the link below if needed:
http://www.malwarebytes.org/mbam/program/mbam-setup.exe