Nothing in the prefs stick out.
So make a backup and then:
Here are 6 prefs related to logins. I suggest you delete them so the system will revert to the defaults once the cache is cleared.
Then, try running through tiki-install.php again and make sure to choose "upgrade" and not "re-install" (which will wipe your data)
The last step of the installer will clear your cache. Perhaps this will help.