Normally four types of errors are not revealed by trial balance. Such errors are:
Errors of omission:
If a transaction is not recorded in books of original entry then both debit and credit effects of the transaction will be omitted and trial balance shall no be effected.
Errors of commission:
These errors are the result of carelessness of accounting staff and in some of the cases such errors do not effect the totals of trial balance.
Such errors neutralize the effect of the errors committed earlier. When one error is committed which affect the total of trial balance but in the mean time another error of opposite effect is committed which neutralizes the effect of earlier error.
Errors of principle:
Whenever any income or expenditure is not properly allocated between capital and revenue, the mistake so made is called a mistake of principle.