I did as you requested, changed the user/password to root in the config.inc.php file.
The error is the same.
I also changed the user/password to something completely wrong.
The error was the same.
In both cases I logged the mysql queries. The log entries were the same message as we have been seeing, no difference.
Is it possible an interface .php file was damaged during transfer/decompress? (just grasping at straws here)