Bank Payment Discount Error

Hi Everyone

i am using Navision 0.4 vendor payment time apply vendor ledger enter Pmt. Discount Date & Remaining Pmt. Disc. Possible but not calculate payment discount

Example Entry Vendor Payment

Open Bank Payment Voucher

Posting Date - 07-08-12

Document - No. BP-00001

Account Type - Vendor

Account No VEN00001

Balancing Account Type - Bank

Bal. Account No.BA0001

then Click Function---- Apply Entry

Select Invoice Number Then Enter Pmt. Discount Date 09-08-12 & Remaining Pmt. Disc. Possible -100

Application - Set Applied Entry

but Below Show column Amount to Apply invoice value 1000 Pmt. Disc. Amount Column Nil

Actual Value 900 Pmt. Disc Amount 100

Please help me

Regards

Vicky