You have incorrectly created and posted an invoice to the system.
If you have entered a Sales Invoice or Purchase invoice in error, the system does not allow you to delete the Purchase Invoice. The method to correct this error is to post a Credit note to balance the erroneous invoice and then allocate the credit note to the invoice.
Please ensure the credit note uses the same date, values, tax and nominal codes as the original invoice you wish to correct.
The procedure is valid on both Purchase Invoices and Sales Invoices.