Customer TDS related issue

While clearing the customer invoice in F-28 when we go Witholding Tax tab and select the line item its not allowing to enter the amount. It should give pop of small window to enter the amount.

Co. code 1000
Customer 1001
WTH Tax Type :- D1
WTH Tax Code :- D1

Customer Invoice posted on 05/04/09 amount Rs. 10,000 through FB70.
In F-28 when trying to clear the payment received and going to witholding Tax tab and double click the line item in which tax amount to be entered.

Gives the follwing error message :-

Message no. 7Q301 Withholding tax information missing from line item

Following possible solution was able to get and tried.
1) GL acct. used for Customer is 134001. In Tcode OB14 Field status variant for Group G001 for Taxes tab is set to optional.
2) As per SAP note 160669 , WTH Tax type has been assigned to the Co. code. Its already assigned to the co. code i.e D1 to co. code 1000.
IMG . Financial Accounting (New) > Financial Accounting Global Settings (New) > Withholding Tax > Extended Withholding Tax > Company Code > Assign Withholding Tax Types to Company Codes