Piwik does not track users on local network

We are tracking three sites with piwk and for a few days everything worked fine. Since a couple of days the hits of internal users (users from our local network with private IP-adress) are not tracked anymore. They appear in apache access.log (as GET … /piwik/piwik.php…) but not in the piwik database. We are just testing, that’s why I don’t know what we have done that special day. Today I made a new Installation (4.2) with the old configs and the problem remains the same. What did I wrong?

Try using something like Firebug and check your HTTP requests to see if there are any errors.

OK, I’ve got it working at least.
I disabled every Plugin, one after the other: GeoIP-Plugin obviously has problems with private adresses.
Not using this plugin solved the problem, but I like this plugin style_emoticons/<#EMO_DIR#>/sad.gif
Does anyone else notice this behaviour and / or has another solution?