GL account is not editable for selecting remaining segments in Petty cash entry -deposit payment against SO

Hi,
We are recently moved on 10.2 from E9. While testing the petty cash entry ,GL account is not editable for selecting remaining segments in Petty cash entry -deposit payment against SO. I have selected the operation- Advance from Customer and got this issue. For other operations of petty cash ,there is no problem for entry.

Please suggest if i am missing anything.