when i try to add foreign business partner in the buy from BP in the RFQ the following message appears (could not insert RFQ lines per Buy- from BP )
reason the tax code field is required in BPs by RFQ LINES

COULD ANY ONE CAN HELP ME
THANKS IN ADVANCE

The BP by RFQ line (that is the BP's quotation) record is generated automatically and there the tax is defaulted. So you have to look into the tax setup for this BP.

check the default tax codes for the BP country and the BP Roles.