I have a John Lewis combination microwave which I believe is made by panasonic. The microwave is brand new and I get a flashing "ErC" message at random on the front panel. Do you know the reason. This is the second machine with the same problem.

I've just fitted a second unit as the first had ErC flashing, you cloud also inadvertently adjust the clock and the clock. JL's initial response was to have me contact their independent engineer (who could not keep the appointment and lied about the reason for not coming). After a brief argument JL sent a replacement, albeit that this took two attempts.
The replacement flashed ErC until the clock was set but now seems to be working properly, also the clock icon automatically dimmed after the clock was set and you can not inadvertently adjust it.
I must say that I'm a bit miffed that JL stated that they were not aware of this fault occurring before, I will certainly think twice before using them again.

I have exactly the same problem with 2 of the JLBICO2 microwave ovens straight out of the box. With the first oven, the service agent who looked at it thought it might be a faulty sensor and recommended replacing this together with the PCU. John Lewis have replaced the first oven and are in the process of replacing the second unit within a couple of days. Hopefully the third time will solve this issue.