Thanks for all the information, I checked the system and found SPK 40 (stock transfer from alt plant) which has the SP as U and plant B.
But can you tell me the difference of using this SPK40 and the one I was trying to use SPK70 which had the tick in the box "Withdr.altern.plant" and Issuing plant as plant B, in terms of postings stock will still be transferred from the same plant.
thanks
Joe