Problem when creating business partner

Dear Expert,

I have a problem when creating business partner from T-code BP

I can't input vendor number in company code header data

The vendor account field is set to required entry.

When create business partner, I make some entry like :

Business partner category : organization

BP Role : Landlord with vendor account

Grouping : external number assignment

Company Code : 1000

The problem is everytime i try to input vendor number, it always failed.

The Vendor account field always display ' <external> '

It's strange.. the vendor field it's seem locked by grouping

What should I do??

___Company Code Header Data___

Company Code : 1000

Customer : <external>

Vendor : <external>

_____________________________

I need your advise.. thank you very much

Thanks,

tweety