QTR-Quadtone RIP

Dear group,

I have been using QTR for a while, but for quite some while now (no 
changes to hardware, or OS which is WinXP-SP2) I am facing problems.

Most jobs will be abortet at some point, either in the very begining, 
or at the last inch of the print. Sometimes in the middle. It is very 
odd, because nothing helps: new driver, re-start of PC, printer 
connected via USB or printer cable. The job starts, and at some point 
it is being interrupted. Afterwards, the printer prints pages of 3-4 
digit codes. I don't know how many, have always switched off before... 
It happens with files of each size, e.g. with the QTR grayscale!

The printer prints well via the Epson driver, and it does print very 
small files (e.g. 500k) via QTR.

Anybody who can help me?
Thanks a lot
Alexander