6 volts can be a pretty big difference and could cause trouble on any computer controlled device. Check that the secondary of a local distribution transformer is bonded and grounded. If there are no distribution transformers the problem might exist right at the main service. It is likely there is a poor bonding or neutral connection somewhere in the system. You should see less than a volt or 2 difference between the neutral and ground but always more than 0 since that would indicate a bootleg ground or other accidental connection between groung and neutral.
