Openfire has one database (either external one like MySQL or MSSQL, or internal/embedded one). So, original version was x86 and was installed in x86. If you ended up with an install folder in non x86, then it might be the case i have described in the guide above. You probably have two installs of Openfire now. And you try to run the new one, which is empty (no database) and that’s why you can’t login, although that doesn’t explain how clients are able to login. You can try running the uninstall in the non x86 folder, then run a version in x86 folder (if it is still there). It probably will be some older version. If it is not there, then that person upgrading Openfire did some stuff, maybe moved files from older installation to new one after the fresh install of 4.2.3 and then deleted the old folder. But maybe not everything was moved and maybe that’s why it gives errors about database.
As this is with external database, maybe when new x64 installer was launched it didn’t find the old installation and it provided the initial web setup and then the person upgrading it pointed to the same database, but it didn’t hook to it normally for some reason.
I guess you can just try to uninstall and wipe all traces of Openfire and do fresh install and try to connect to the same database. If you have database credentials.
Also, make sure you don’t have two instances of Openfire running as it might already be running as a service.