HTTP code 400 (3 replies)

I am using Drupal with the Piwik Web Analytics module and when saving the configuration I am getting

/statz/piwik.php failed with error "Bad Request" (HTTP code 400).

Now the oddd thing is that I get the same error from an existing site that is runnng and delivering data to the piwik instalation

Are there any permissions I should check, what permission should index.php be?

If I go to the url/ ~ /statz/piwik.php I see a page with - Piwik is a free/libre web analytics that lets you keep control of your data.

Thanks