I have the same problem here:
Error while trying to connect to the MySQL database:
No entry is registered for key ‘db’
My webhoster ist 1and1. They use the following construct for the mysql servername when you use a mysql 5 database:
Maybe this is the problem. But i had never any problems with this in the past. Used it on Wordpress and Typo3 installations.
Furthermore I have to turn on the usage of PHP 5 (instead of 4) using the .htaccess file. This is done with the following code:
# PHP5 anschalten fuer 1und1
AddType x-mapp-php5 .php
AddHandler x-mapp-php5 .php
Normally file restrictions are ok on the 1and1 server. After the ftp upload all files are set to 644 and all directories have 755. Just to be sure I chmodded the config and tmp directories to 777. But this did not help.
Hope you find a solution soon. I really would like to use piwik.