Hi Mr. Murthy,
The GTS Document Type that is mapped to your P.O. Type (e.g. 'IMPORD') must be activated for Customs Management. Technically, that's to say, there must be an entry in table /SAPSLL/TLECHS with 'LECCUS' assigned for that Document Type.
If that's the case, then you should be able to create an Import Declaration before GR irrespective of the situation with the IBD.
Come back for more assistance if you need it.
Regards,
Dave