How can you define an error of commission ? Be more precise

Mr. Frank has a good answer 

Error fo commission means that an item has been recored to the correct category of account but the wrong account. for example if we received $500 from customer X and the accounts receivable credited the amount to customer Y. In such a case he should make the following correction:

AR - customer Y       500 (DR)

AR- customer X         500 (CR)

Error of commission are where the bookkeeper makes a mistake in carrying out his or her task of recording transactions in the accounts.Two common types of errors of commission.

   1. Putting a debit entry or credit entry in the wrong account . e.g if telephone expenses of $ 540 are debited to the electricity expense account ,an error of commission would have occurred.

   2. Errors of casting (adding up) eg the total daily credit sales in the sales day book should be $ 28425 but are incorrectly added up as $28425.