I have Windows Vista Home Basic and Keepass Password Safe v2.20. I have been using KeePass for a long time without any problems. The application is set to ask for a change of the master password and the key file yearly. I have made these changes, the master password remained the same but I think I made a mistake and for the key file I set the Password Safe database file (kdbx) by accident. After I had to save changes in the appliacation. In this situation the key file changes without any "undo" possibilities, and when I wanted to access next time the program said the composite key is invalid.
If a user does not backup the database, he has loose accees forever easily and no chance to recover/restore previous kdbx file version.