There are a number of errors that might have been made that do not prevent the trial balance from agreeing. These are:

Errors of omission, where a transaction has been completely omitted from the ledger accounts.

Errors of commission, where one side of a transaction has been entered in the wrong account (but of a similar type to the correct account, for example, entered in the wrong receivable’s account, or in the wrong expense account).

An error of commission would not affect the calculation of profit, or the position shown by the balance sheet.

Errors of principle. As for errors of commission, but the correct and incorrect accounts are of different types, for example, entered in the purchases account instead of a non current asset account. This type of error would affect the calculation of profit, and the position shown by the balance sheet.

Errors of original entry, where the wrong amount has been used for both the debit and the credit entries.

Reversal of entries, where the debit has been made to the account that should have been credited, and vice versa.

Duplication of entries, where the transaction has been posted twice.

Compensating errors, where two or more transactions have been entered incorrectly, but cancelling each other out, for example, electricity debited with $100 too much, and sales credited with $100 too much