Prd2010, why don't you download the AVT Hex Terminal software and see if you can talk to the box that way? If it connects with Hex Terminal then you know the COM port is configured correctly and your computer can talk to it.

If you can talk to the AVT box, and everything else in DHP works (opening BINs, etc) except for cable registration, then it's related to whatever isn't being done by AVT now to make the boxes compatible with DHP.

Easiest place to start.