Hello Rajat,
I've faced the same issue.
See it may be because of conversion factor you used in material master which you're going to purchase.
For example, You maintained 14.8 kg = 1 Nos in purchase order.
While you take GRN 65.050 kgs, in excise tab you will see 0.004 kg open qty after post that document.
In that case we need to remove that conversion or make it same 1 kg = 1 nos. then it will allow to post properly.
Hope it will help you.
Thanks,
Nilesh M.