Other Exception in period close exception report

Hey guys ! wish that you help me in this regard. I gotta close the payable period but when I went to do so It won't let me when I open period close exception report there is nothing I found Unaccounted except the one which fall in the area of 'Other Exception'. I note the invoice number and went to Invoice workbench to check any error but I found nothing in it except there were just one Item line created for which there is no WHT code had applied and two Withholding Tax line were entered manually, Accounting has already been generated for this invoice and apparantly there is no fault poping up. How would I