It seems to be a google chrome issue? http://www.google.com/support/forum/p/Chrome/thread?tid=19043fff689eff09&hl=en

http://drupal.org/node/1048140

and MANY more. please have a look as this is probably not a piwik bug (if you find out this is a piwik bug please post a comment)

Sorry, I've never encountered this error message, and as far as I know the error message doesn't originate with Piwik, PHP, or MySQL.

Hi the problem is not with a browser (same problem in firefox and IE). But I have identified it.

The problem is due to permissions, restoring 777 to all files (such a high permission is required by my server) fixed it. I suspect something goes wrong with the cron job or another aspect of piwik which messes it up if permissions are incorrect.

I refer you to my original post where i said it worked fine at first, something must have happened to make it not work a few hours later. The problem is then the automatic update causes the new files to have incorrect (lower) permissions which need manually changing.

At minimum, I would have expected an error message.

For our reference, can you lower the permissions and use "curl" to capture the HTTP response (header and body)? And please see if there were any error messages in your web server log file that might identify where the issue occurred. Thanks.

Hi, sorry i cant replicate the error, changing permissions back gives the message that some files aren't writeable. I didnt check permissions before i changed them so i don't know which files had what.

The error log however shows these (lots of the same message with differing pid's up until i changed permissions)

Mon Apr 18 17:39:54 2011] [warn-phpd] mmap cache can't open /home/greensky/public_html/piwik/tmp/cache/tracker/1.php - Permission denied (pid 3520)

Interesting. I didn't know we used the mmap cache.

I have run into the same problem and after check the config for a while , I found the solution.
the question is nothing to do with the piwik, but the nginx config. From the offical nginx conf, I found a line like this

location ~* ^.+\.(?:jpg|png|css|gif|jpeg|js|swf)$ {
  # Defining the valid referers.
                  valid_referers none blocked *.piwik.com   othersite.com;   //change this line to deal question
                  if ($invalid_referer)  {
                          return 444;
                  }
                  expires max;
                  break;
         }

when we add tracker to the other site for tracking . the application will get the piwik.js from piwik application. and if this conf doesn't contain the refering url . the nginx will reject this request and return http code 444. my solution is add the valid url here . and the error disappear.

Hi @digjack in order for your comment to help everyone who could benefit, do you mind reporting it to the project directly here: https://github.com/perusio/piwik-nginx/issues