I have a couple of questions, are you just now starting to use the reg.? If using it before, what happened to change this. My first thought is that there may be a hardware problem but to prove it we must restart the system as if taking it out of the box for the first time. Do you have the manual for the 390?
Have you tried to RAM Clear it yet? It will destroy any programming done before and all totals, that's why I asked the first question.
Yes, tried a RAM clear, and took a day reprogramming.
There must be a fault in the memory module. Csn you program around it , say by using very different number of PLUs? Leave 6 & 7 and go on to other PLUs, even if you have to manually enter them...