To fix this issue download the hotfix titled Smith_BuyNow.dll.zip dated today from the cart downloads page.  Also, open up the "Smith_AddProducts" stored procedure on the last line of the sproc add "select @myProdID".  The updated stored procedure is as follows:
 
ALTER PROCEDURE [dbo].[dnn_Smith_AddProducts]
    @CategoryID int,
    @Manufacturer nvarchar(50),
    @ModelNumber nvarchar(50),
    @ModelName nvarchar(200),
    @ProductImage nvarchar(500),
    @ThumbnailImage nvarchar(500),
    @UnitCost money,
    @MemberPrice money,
    @QuantityOnHand int,
    @Summary nvarchar(1000),
    @Description ntext,
    @DownloadUrl nvarchar(1000),
    @Featured bit,
    @Archived bit,
    @weight decimal(12,5),
    @sortOrder int,
    @ExcludeCoupon bit ,
    @Items int,
    @Share bit,
    @TabModuleId int,
    @CreatedByUser nvarchar(100),
    @CreatedDate datetime,
    @LogicallyDeleted bit,
    @Recurring bit ,
    @SubscriptionInterval varchar(50) ,
    @RecurringOccurances  int ,
--    @RequiredProductID int ,
    @UrlGUID varchar(50) ,
    @EncryptUrl bit,
    @AddDnnRole varchar(50),
    @RequireLogin bit,
    @UsePriPriceWght bit,
    @bundleID int,
    @masterBundleID int,
    @RoleExpireDays varchar(50),
    @SubCategoryID int,
    @TaxExempt bit,
    @PortalID int,
    @AffiliateUrl nvarchar(1000),
    @RequireCoupon bit,
    @ShowPDUDF bit,
    @AutoGUID bit,
    @Description2 ntext,
    @Description3 ntext,
    @Description4 ntext,
    @Description5 ntext,
    @TabName1 varchar(50),
    @TabName2 varchar(50),
    @TabName3 varchar(50),
    @TabName4 varchar(50),
    @TabName5 varchar(50)
AS
INSERT INTO dnn_Smith_Products(
            [CategoryID]
           ,[Manufacturer]
           ,[ModelNumber]
           ,[ModelName]
           ,[ProductImage]
           ,[ThumbnailImage]
           ,[UnitCost]
           ,[MemberPrice]
           ,[QuantityOnHand]
           ,[Summary]
           ,[Description]
           ,[DownloadUrl]
           ,[Featured]
           ,[Archived]
           ,[Weight]
           ,[SortOrder]
           ,[ExcludeCoupon]
           ,[Items]
           ,[Share]
           ,[TabModuleId]
           ,[CreatedByUser]
           ,[CreatedDate]
           ,[LogicallyDeleted]
           ,[Recurring]
           ,[SubscriptionInterval]
           ,[RecurringOccurances]
           ,[UrlGUID]
           ,[EncryptUrl]
           ,[AddDNNRole]
           ,[RequireLogin]
           ,[UsePriPriceWght]
           ,[BundleID]
           ,[MasterBundleID]
           ,[RoleExpireDays]
           ,[TaxExempt]    
           ,[PortalID]
           ,[AffiliateUrl]    
           ,[RequireCoupon]    
           ,ShowPDUDF
           ,AutoGUID
           ,Description2
           ,Description3
           ,Description4
           ,Description5
           ,TabName1
           ,TabName2
           ,TabName3
           ,TabName4
           ,TabName5
                   
) VALUES (
    @CategoryID,
    @Manufacturer,
    @ModelNumber,
    @ModelName,
    @ProductImage,
    @ThumbnailImage,
    @UnitCost,
    @MemberPrice,
    @QuantityOnHand,
    @Summary,
    @Description,
    @DownloadUrl,
    @Featured,
    @Archived,
    @weight,
    @sortOrder,
    @ExcludeCoupon,
    @Items,
    @Share,
    @TabModuleId,
    @CreatedByUser,
    @CreatedDate,
    @LogicallyDeleted,
    @Recurring,
    @SubscriptionInterval,
    @RecurringOccurances,
--    @RequiredProductID,
    @UrlGUID ,
    @EncryptUrl,
    @AddDnnRole,
    @RequireLogin,
    @UsePriPriceWght,
    @BundleID,
    @masterBundleID,
    @RoleExpireDays,
    @TaxExempt,
    @PortalID,
    @AffiliateUrl,
    @RequireCoupon,
    @ShowPDUDF,
    @AutoGUID,
    @Description2,
    @Description3,
    @Description4,
    @Description5,
    @TabName1,
    @TabName2,
    @TabName3,
    @TabName4,
    @TabName5
)
DECLARE @myProdID int
SELECT @myProdID=scope_identity()
INSERT INTO dnn_Smith_CategoryProduct(ProductID, CategoryID) VALUES (@myProdID, @CategoryID)
IF (@SubCategoryID IS NOT NULL) and (@SubCategoryID <> '') and (@SubCategoryID <> 0)
 INSERT INTO dnn_Smith_CategoryProduct(ProductID, CategoryID) VALUES (@myProdID, @SubCategoryID)
 
select @myProdID