QTR-Quadtone RIP

I use QTR with an Epson R1800 on an iMac G5 Power PC and have recently run into this 
problem:

The printer prints nozzle checks, but when I send a file to the printer, nothing happens. The 
printer window tells me that it's printing and tallies up the percent completed, up to 100%, 
but nothing prints. Then, when it reaches 100%, the printer feeds through a blank page.

I have tried uninstalling and reinstalling the Epson driver and the QTRIP, but unless I did so 
incorrectly, that wasn't the root of the problem. I have also tried replacing the USB cable with 
another USB. to no avail. I haven't tried Firewire because I understand that QTR doesn't like it?

When I select the Epson R1800 as my printer without specifying that it use the QTRIP, the 
printer will actually print the image. But of course it doesn't look right (way too dark) because 
it is running without the proper curves.

Has anyone run into this problem? Any advice?