26 AS on TDS Credit

Dear All
 
I have received a tax credit statement 26 AS from IT in which some of the TDS deducted by Employer has been shown as "U" i.e. unmatched.
I request all of you to suggest
1) how to give reply on this to IT and to Employer.
2) Is it the duty of employee to get a confirmation from the Employer ??
3) How the empolyer will get a confirmation again ( and from whom) as he has already having a acknowledged/stamped challan showing that he has already made the payment.
 
Kindly need your suggestion on liability of  Employee as well as employer and how to sort this problem??