Dear Arshad,
As João Paulo Campos Amaral de Almeida stated that are you using Profit Center scenario?
I think you are using profit center scenario where giving profit center is one of the mandatory criteria.
Now in your case i would suggest that please check the GL's involved in your case and go to create/bank/interest tab and check the Field status group there.
Now go to T code OBC4 and click on the field satus group of your GL and check there for profit center.I think it is in supressed mode change it to mandatory field then you will be able too see the profit center field in line item 001.
PS:Please don't deactivate document splitting in PRD otherwise it is going to bring inconsistency of data.
Hope this will help you to solve your issue.
Regards
Eugene