Only intranet visits tracked

On my Joomla I have installed Piwik V3.02 and nfrPiwik plugin. On my homepage the piwik tracking code is correctly included (it shows when looking at the source). Joomla and Piwik is installed on a NAS Server. My visits within the intranet are correctly counted, but no visits from the extranet are counted. When looking at the file requests and response codes from a website speed test site, it shows a connection error from piwik.js.
Piwik is installed on a subdirectory of the Joomla installation.

What could be causing this error?
Thanks for any help.