Cause
This error occurs as the check box In case you do not have Invoice wise details you can check this checkbox to go to the table below to fill in the Customer wise consolidated/summary details of Sales is selected by default. Since Tally.ERP 9 exports data invoice-wise, posting data to annexure is disallowed. This behavior is noticed in version 4.6 of VAT excel template published on 19th Jul '16.
Solution
Uncheck the option In case you do not have Invoice wise details you can check this checkbox to go to the table below to fill in the Customer wise consolidated/summary details of Sales.
Export the data to the annexure.