high earth to neutral voltage

I'll go along with PW

There shouldn't be any. Neutral is a conductor carrying the return current, or the vector sum of all the phase currents in a multi-phase system, and Earth is a protective conductor that doesn't generally carry any current except briefly as is required under fault conditions in order to operate the circuit protective device.

Please define "high".

High neutral to earth voltage is of concern only in those electronic systems which are communicating amongst themselves. Because, to be economical, the data zero reference is taken from the ground or earth only. If there is appreciable difference in the ground to neutral voltage then there would be communication data errors.

One need not believe that high neutral to earth voltage is dangerous for all computers. It is not true. Because, in India, most of the domestic electrical installtions do not have an earthing system at all. Still, computers have been in operation in these houses for years now.

<...If there is appreciable difference in the ground to neutral voltage then there would be communication data errors....>

Even if the communications circuit supply were downstream of a power step-down isolating transformer and incoming supply neutral wasn't linked to the 0V rail downstream of the transformer _{[learing experience for PW, please]}?

If you use an isolating transformer with no neutral bond or earth bonds between the two systems, then there will not be any communication errors. But, in such a case, there would not also be a high Neutral-Earth Voltage. Most of the neutral to earth voltages are encountered in power system grounds only. They may not be experienced in communication systems.