Faulty 1 to 9 DVD duplicator

Dear Nick, On Going fault. We have spoken before about this particular machine. It is a Stordigital DVD duplicator 1 to 9 with 160gb h/disk. Serial number of unit is 001592. Basically problem is that it fails / locks up during burning runs. We put in 10 dvds (verbatum 8x) and first thing in the morning it will produce approx 50 discs successful (5 runs of 10). It will then start failing as it will for the rest of the day. Normally one DVD writer - which varies each time fault occurs, will lock up with a solid green light. This lock up will cause burning counter time estimate to freeze on a certain percentage (usually 0%) and the unit will have to be turned off at mains to regain control. Once machine is back on again, all discs will eject and will have been written to slightly depending at what %age it locked at. The 10 discs will get binned and we start again. It may work for another 1 or at most 2 runs of 10, before it fails, but sometimes it will just fail continually from then on unless we power down for several hours or leave overnight. I have adjusted burn speed and it is set to 6x, since our last conversation a month or so ago. Normally duplication jobs are relatively small runs of upto 100, so we put up with problems. It is only every now and again we get over 1000 discs to do, as is the case now, when we get frustrated with the failure rate. I think it is running firmware 1.61d.