Well, i uninstall using the code provided on "uninstall.sql", and try to install again, but after paste the code and send it, it gives me this error (always the same error)

8 statements processed.
ERROR: Cannot insert configuration_key "" because it already exists
Warning Note: 1 statements ignored. See "upgrade_exceptions" table for additional details.
This sounds strange because I did uninstall the old version and then installed the latest version. I didn't get any error. It looks like you didn't delete the tables properly. That's why when you tried and reinstalled it won't allow duplicate. Did you delete all the related files and run the uninstall sql file in Admin > Tools > Install sql patches? You might want to try manually deleting them in the phpmyadmin. Good luck.