Vendor did not replicating to SC

Hi,

I have an issue while creating shopping cart from a perticular Internal catalog.

I have selected 4 catalogs items from the Internal catalog. while After ordered the SC the system created a Purchase requisition in the backend R/3 instead creation of the PO and the vendor code disappear. Though the vendor was there in the item present in internal catalog.

Can you please help me why did this occur? Where might be going wrong with this?

Thanks a lot in advance...

will be rewarded if the solution will work..