Nick,
It is sad. The AuthenTec code (HP SimplePass Versions 6.x) seems unable to make the leap to Windows 8.1.
Hopefully you know your passwords or you have another Windows 8 machine from which you can retrieve them.
You might try the newer version of HPSimplePass version 8.x ** as suggested in
Simple Instructions to Upgrade HP SimplePass
** At writing, "new" version is HP SimplePass 8.0.0.51
One of our Experts does have this new HPSP version running on his Windows 8.1 system. You may have success, too.
You will have to remove HP SimplePass V6.x before you install version 8.x. You will not be able to use your .tsd file to recover your Webcards that was used with the older SimplePass. Short Answer "why not": The code is different in the new version.
HP SimplePass V8.x does have an Export process. Once you go through the pain of setting up your webcards from scratch, you will be able to Export the webcards to an .opi file; you can later use that to Import the webcards should that be necessary.
Some model notebooks can sometimes use the aforementioned "Windows only" native fingerprinter logon software in Windows 8.1. Track back through this thread for more information. The "native" logon option does not provide for website logons.