I just upgraded my ST server to 7.5.1 and had the same problem. It was working just fine prior to the upgrade. It seemed that stlinks.js file get updated and the 2 var files weren't in there anymore. Once I added the 2 lines again, everything is working fine. Have you copied the 2 line in the hostinfo.js to the Stlinks.js? Make sure they look the same on both the ST server and the DWA server.
Here is the technote on what I did:
http://www-1.ibm.com/support/docview.wss?uid=swg21225540