GET request to piwik.php failed. Try whitelisting this URL from mod_security and HTTP Authentication.
I put in a ticket at Servint about the mod_security, they said it was not running on my server. Their tech support attempted to install Piwik and was seeing the same error. They said they have installed it many times before and this is the first time they have seen this.
I went ahead and clicked next and went through the rest of the process, setup a site, put the code in the footer, but it gives an error saying it can't connect.