In case you get one of these messages and you don't know what it is:

A change has been made to improve security.
You now have only one password, that you use for the website.
In game, you use an "unlock code" instead of your password.

How to use your unlock code:

I recommend first installing the new test patch which has better support for the new unlock code.
Test patch: https://www.lfs.net/forum/thread/110607

Then...
1) Visit details page
2) Click: send email with a new unlock code
3) Get email
4) Paste code from email into LFS "GAME password" (or "Unlock code" in the new test patch)
5) Click unlock

The "GAME password" or "Unlock code" field is in the LFS unlock screen, accessible by a button at the bottom right of the entry screen.

For information about this change, please read this thread: Removal of WEB password and GAME password