MRP uses special procurement type L for material .ME174

Hi All:

   1 .When I tried to create PO for non-valued  material,SAP displayed message "MRP uses special procurement type L for material"- .ME174.

    (Non-vaued material is customized material type which has no accouting view and  is supplyed by suupplyer for free.)

   2.I checked  the material setting in MM03 finding that the Procurement type has been set as 'F' and the Special procurement has been set as '30'.

   3.I checked  the SPRO finding that the setting as  following path finding that Special  procurement has been set as L.

    IMG > MM > Consumption-Based Planning > Master Data > Define Special Procurement Types

   So what other problem is with my setting or configuration?

  Thanks.