"Errors in metering" was meant as a very broad statement. I agree that modern meters are reliable. An error in metering could include misreading such as switching your meter reading with another one - not hard to do in large meter banks. Some tenant metering systems do not use "utility" type meters and these are prone to errors. Another common problem is supplying "energy" to users outside your control - sometimes by accident. In an apartment building an electrician could accidentally tie in to the wrong main panel. I know of one tenant who was paying for his neighbor's refrigerator. Figured it out when he was away for a month, turned all his stuff off and his bill/meter reading showed abnormal consumption. Lacking any specifics all I/we can do it toss things out there.