Funds Mangement - Fund center derivation error at the time of PO/MIGO

Hello -

Generally ,If FM account assignements are available in purchase requisition , same should be carried to purchase order and to the good receipts. But I am getting an error at the time of PO or MIGO that " Fund center not derived'. Why is this happening ? What can I do to avoid this problem. can I create a step in the derivation to keep the original FM assignments from the previous documents....is there something to do with field status??

Thanks in Advance

Chris