I. View previous sales bill- If you able to view the bill-It is not a Software problem.
II. Find out the column- Which column is not able to enter the data- If the curser is in customer field, you have to check customer master field-Allow billing option. If the curser is in Quantity, Batch, Expiry and tax, you have
to verify Product master.
III. You can see the bottom of the message-You can easily find out your problem.
IV. If you have any error message in billing screen - Double click on I Con symbol for repair the database.