QTR-Quadtone RIP

Hi Roy,
I've been using QTR for a few years now, never had any problems and I 
have always been pleased with the results.  After a lull of a few 
months I have just reinstalled on my new machine and I'm experiencing 
some very wierd problems.  In a seemingly random fashion, sometimes I 
send a print and while the printer seems to be diligently following the 
instruction with the printhead moving over the paper it is supposed to 
be covering, it is not actually laying down any ink.  I use a Epson 
2100 with UC inks connected to a PC running XP SP3, with all the latest 
patches.  
At first I thought there may be a bug with 2.6.2, however when I 
uninstalled and reinstalled 2.5.2 but had the same problem.  I was 
hoping you might help me identify the problem!
Many thanks!
John