Certain errors will not affect the agreement of trial balance. Though such errors occur in the books of accounts, the total of debit and credit balance will be the same. The trial balance will tally.
Examples of such errors are as follows: 
(i) Treating revenue expenditure as capital expenditure
(ii) Omitting a transaction completely
(iii) Entering a transaction in a wrong subsidiary book
(iv) Entering a transaction twice in a subsidiary book or journal
(v) Entering the amount of a transaction wrongly in the journal
(vi) Entering the amount of a transaction wrongly in a subsidiary book.

It means the mistake committed in the application of fundamental accounting principles in recording a transaction in the books of accounts.
The following are the possibilities of error of principle:
(i) Entering the purchase of an asset in the purchases book:
Example: Machinery purchased on credit for Rs. 10,000 by M/s. Anbarasi garments manufacturing company entered in the purchases book.
(ii) Entering the sale of an asset in the sales book:
Example: Sale of old furniture on credit for Rs. 500 was entered in the sales book.
(iii) Treating arevenue expenditure as a capital expenditure:
Example: All amount of Rs. 2,000 paid for repairs to a machine is debited to machinery account.
(iv) Treating a capital expenditure as a revenue expenditure:
Examples: An amount of  Rs. 3,000 spent on the construction of an additional room is debited to repairs account.

Note: Method of deriving the rectifying entries

Note: Method of deriving the rectifying entries

(a) Depreciation account should be debited with Rs. 5,000.
(b) Wages account should be credited with Rs. 2,000.
(c) Nila account should be debited with Rs. 50.