Thanks Timo! Indeed, adding the full URL to the tracker does the trick.
But your second comment is a problem for me. I have multiple web sites in Piwik, and I would really like to see the overlays for all web sites, without the need to log in again (and again, and again) using a different URL. I guess more people need this. I have set enable_trusted_host_check=0, but that doesn’t make a difference.
[quote=Hark]
Thanks Timo! Indeed, adding the full URL to the tracker does the trick.
But your second comment is a problem for me. I have multiple web sites in Piwik, and I would really like to see the overlays for all web sites, without the need to log in again (and again, and again) using a different URL. I guess more people need this. I have set enable_trusted_host_check=0, but that doesn’t make a difference.[/quote]
Your exact situation on how you track you stats is not clear to me,
but why no set up a sub domain for trekking all your sites?
Thats what I do, and other amins can get acces and see only there domains.
I agree. Sounds like you could simplify your setup and use a common domain for tracking all websites.
Matching the referrer with the tracker URL is how the tracker detects that the session should be launched. So there’s no simple fix for this issue.
We are planning to add other ways to launch the session but there’s no timeframe for that yet.
True, I could use a common domain. But then Piwik will use third party cookies and I would like to prevent that (for example I know people, including myself, that block third party cookies. It’s a Firefox setting)
Now working, thanks 
IF you setup piwik on a different domain it will NOT use third party cookies. Piwik only uses 1st party cookies by default
You are completey right matt, I didn’t know that. Now I use the default tracking code again.
However, now the Page Overlay doesn’t work anymore. I cleared my browser cache, and my Piwik domain matches the one in the tracker code. But I get “The Page Overlay session couldn’t be launched yet.” every time.
Well, my mistake (again). I have www.domain.com in the tracker code but visited Piwik on domain.com (without www). That doesn’t match of course. Now I use www.domain.com and it works!
I get the same error “Session could not be launched”. Can someone tell me which version of jquery is required by overlay as my site is currently using jquery 1.3.2 which may be too outdated…
Can you check whether you get Java Script errors? If you do, please post them so I can tell you whether it’s realted to jquery. If you don’t, it’s not related to jquery.
That’s just a warning and it’s not related to Page Overlay. This warning is triggered because the regular Piwik Tracker checks whether the parent frame has a referrer. It doesn’t cause any problem, it’s just a warning.
So if that’s all you get, it’s not a Java Script issue. Please follow the troubleshooting guidelines: Page Overlay – Visitors Click Map - Analytics Platform - Matomo
The most likely cause is that you have an old version of piwik.js (the tracker code) cached. Please clear your browser cache.
Thank you Timo.
However, I already cleared the cache of my browser (Chrome) and Drupal 6 several times. Is there anything in the new tracking code that can be recognized as necessary for overlay?
This is the currently used code:
<!--//--><![CDATA[//><!--
var _paq = _paq || [];(function(){var u=(("https:" == document.location.protocol) ? "https://piwik.mydomain.de/" : "http://piwik.mydomain.de/");_paq.push(["setSiteId", "2"]);_paq.push(["setTrackerUrl", u+"piwik.php"]);_paq.push(["trackPageView"]);_paq.push(["enableLinkTracking"]);var d=document,g=d.createElement("script"),s=d.getElementsByTagName("script")[0];g.type="text/javascript";g.defer=true;g.async=true;g.src=u+"piwik.js";s.parentNode.insertBefore(g,s);})();
//--><!]]>
Have you followed everything on the troubleshooting page? If not, please do.
Are you sure you have deleted the temporary files in the cache? When you click “clear all browsing data” in Chrome, the box “Empty the cache” needs to be checked before you click “clear browsing data”. It’s easy to miss that the box is not checked.
If you did that correctly, maybe it is related to jquery after all. Can you try to use a later version of jquery, clear your cache and try again? You can then switch back to the old version, I just want to know whether it would work this way.
Yes, I followed everything from the troubleshooting page before posting here.
I cleared “history, downloads, cache, cookies”.
Unfortunately jquery 1.3.2 is the latest jquery version available for Drupal 6 (see jQuery Update | Drupal.org).
Is there anyone else with a site using jquery 1.3.2 and got overlay running?
Could you maybe just replace the file that comes with drupal with a later version of jquery? It’s just for testing, you can switch back to the old version after one try.
Ok, I did it. After that I got some errors related to Drupal’s javascript (which may be the cause, why 1.3.2 is the latest available version…) and overlay mode still failed.
I just replaced jquery on one of the websites I’m tracking with version 1.3.2 - it works. So that’s not the problem.
When you clear the cache in Chrome, you also have to select “from the beginning of time”. Did you do that?
Also, can you please try a different browser? Also clear your cache there.
If none of that works, things will become complicated…
Yes, of course I cleared from the beginning of time. It also doesn’t work with Firefox 18.0.2
If now all obvious things can be excluded, the problem may lie on the Drupal side. I’ll wait to see what other people experienced there…
Thanks anyway, Timo!
Finally, someone found the problem:
Drupals Piwik module was/is pushing the SiteId as string: _paq.push([“setSiteId”, “2”])
However, Piwik checks it using !== against a number, which always fails because it’s compared against a string.