QTR-Quadtone RIP

Just downloaded QTR after seeing it mentioned on the Luminous Landscape Video with 
Brooks Jensen.  I immediately experienced improved B&W printing but am just beginning to 
explore the possibilities.

My problem is that when I wanted to print a color image today, I changed all the settings 
back to the Epson 2400 and when I print I get a "communications error" message.  I have 
checked everywhere I can think of to see if I am missing a printer selection, and I can print 
the same image in B&W with ease.  I have turned off the printer, the computer, etc.

I'm using a G5 and Epson R2400.  Any suggestions?

Thanks in advance.