I think you have some wrong info.. .or I do.
The 541 is a single core hyper threaded processor and not a dual core. So no D in its name.
The P4 640 is not a dual core either but does have hyperthreading also. It has 2Mb of l2 cache instead of 1 that the 541 has.
I see no other difference myself. Thats a strange problem you have.
I found thier spec page and the 40 is not on their processor list.http://www.cyberlink.com/stat/oem/directv/dtcp-ip-advisor/enu/troubleshooting.jsp