The following error has occured during databaseSetup-phase of PiWik installation:
Error while trying to connect to the Mysql database: SQLSTATE  Access denied for user 'xxx'@'localhost' (using password: YES)
Switching mysql-server from localhost to 127.0.0.1 does not help - it only generates the same error.
I am running Piwik on a shared-hosting solution without permission to change MySQL socket access rights, making this a show-stopper for my Piwik installation.
Try logging into the database from the command line (using "mysql"). If that fails, then it could mean your database and/or database user wasn't properly created.
This is not a Piwik problem: it looks like your user doesn't have permission to connect on this mysql server. please make sure your server adress, login, pwd are all correct.
Issue resolved: Typed 127.0.0.1 instead of localhost and installation works fine now.
If this is a common issue, I would suggest providing users with contextual help in installation program, or automatically resolve localhost to 127.0.0.1 in Piwik.