Some of the common errors leading to mismatch between Form 26AS and Form 16 are as follows:
•    Non-filing of TDS return by Deductor
•    Wrong PAN number of the employee quoted by the Deductor.
•    Wrong PAN / TAN of Deductor / AY quoted
•    Wrong Challan Identification Number (CIN) of TDS payment quoted in TDS Return
•    Omitted detail of TDS payment
•    Challan-wise annexure in TDS Statement does not mention details of the employee (e.g., name or gender)
•    False / Excess TDS amount claimed in the return.
Compare the figures in Form 26AS with that of Form 16 and Form 16A. Mismatches between your Form 26AS and Form 16 or TDS certificates may lead to less refund or more taxes payable. If you find that any of the above details don’t match:
•    You need to inform the party responsible for deducting TDS from your income (i.e., your employer).
•    The employer has to file a revised TDS Return. Ensure that the details are correct in the revised TDS return to avoid another mismatch.