The cause of this issues, may be the back end update which you did on while posting the invoice.
Resoulution:
1. Open reconcile (Tools-->Utilities-->Purchasing-->Recocile) window.
2. in Recocilation window, choose only the "Print Report" in option tab to verify whether the invoice will correct or not. If, the invoice applied amount corrected then choose "Reconcile" option to process the reconcilation.
Hope this helps!!!