I also have a PT50C, have had it less than 2 years and it's needed repair 3 times.
1st time it said the neutral and ground were reversed when the source was fine, next time it seemed to work OK but had EEEE in the readout, the last time it said the power source was too low, 80 volts, my meter confirmed the source was fine.
Both of the last times the tech argued with me, said the PT50C doesn't ever say EEEE and the last time he said my meter was wrong because they calibrate it before they ship them from the factory.
all 3 times they did repair it under warranty but the last 2 times i had to ship in and be without while they repaired it.
I've read a bunch of great things about Progressive Ind and their products so I'd like to think I just have a bad unit.