Which of the following errors is an error of principle?

• A. Total sales figure was taken as ` 19,373 instead of ` 19,733
• B. A discount of ` 30 allowed to Mr. A was not recorded in the discount allowed account
• C. Legal charges for acquisition of building for ` 500 was entered in the Legal Expenses Account
• D. 1,000 received from Mr. X was posted to the credit of Mr. M