The error is here:
SET @Result = (SELECT T0.[Substitute] as LieferantenArtikelNummer, T0.[U_NF_Supp_VPE] as Verpackungseinheit, T0.[U_NF_Supp_ME] as Mengenseinheit FROM OSCN T0
WHERE T0.ItemCode = @ItemCode AND T0.CardCode = @CardCode)
If you are setting a variable your select can't return more than one field.
Regards
Diego