I moved ZP to a new account on the same server due to ajaxmanager vulnerability. On the old account I upgraded step by step to the newest version and all worked fine. Then it stuck me again and almost every header of every php file got infected. I decided to move the installation to a new account I opened.
I exported DB on the infected account and imported it to a newly created empty DB on the new account. However when I run setup I got this error:

"Zenphoto encountered an error
MySQL Error: The database is connected, but MySQL returned the error Access denied for user 'xxxxx'@'localhost' to database 'xxxxx' when Zenphoto tried to select the database xxxxx."

What would cause this error?

This error message comes directly from MySQL. It means just what it says--MySQL has denied access to the database. Most probably because the user credentials are not correct.