Roger,
Whilst I don't use the DSUSB (do use the DPUSB, though), I have had similar issues using DSLR Focus. With the data USB cable from the laptop to the camera and a home-made serial cable (USB-to-serial adapter-to-headphone jack) for the shutter release control.
I found that I had to sometimes use a different USB port for the serial release cable, and, ensured that DSLR Focus had the right COM port associated with it that was found through the Device Manager (advanced properties for USB-to-serial device).
Also, just double check which type of communications mode your camera is in. I think it's found in the last menu.
I'm sure you've tried these ideas already -- just thinking out loud. These are the worst problems as they're temporal -- you'll try again tomorrow and everything will just work.
Let us know how you go.
Regards,
Humayun