The tunneling DLL is a library that adds tunneling to a QlikView setup where you use IIS as web server. The QlikView Web Server has tunnelling support builtin. The tunnel is necessary when the IE-plugin cannot reach the QlikView Server directly through port 4774 (= qvp:// port).
OTOH, it seems that the Tunneler is installed, but the browser has no idea what to do with the data arriving through the network. Did you first install the IE-plugin on the Windows machine of both your client and your co-worker?