I finally got this proc to work, but had to modify the code (marked in red) to get it to work.  This was running the script directly in SQL Express, I did not try running it under the Host/SQL in DNN.

SET QUOTED_IDENTIFIER ON
GO
SET ANSI_NULLS ON
GO

create procedure dbo.dnn_FindBanners

@PortalId     int,
@BannerTypeId int,
@GroupName    nvarchar(100)

AS

SELECT  BannerId,
        dnn_Banners.VendorId,
        BannerName, 
        URL,
        'ImageFile' = case when dnn_Files.FileName is null then dnn_Banners.ImageFile else dnn_Files.Folder + dnn_Files.FileName end,
        Impressions,
        CPM,
        dnn_Banners.Views,
        dnn_Banners.ClickThroughs,
        StartDate,
        EndDate,
        BannerTypeId,
        Description,
        GroupName,
        Criteria,
        dnn_Banners.Width,
        dnn_Banners.Height
FROM    dnn_Banners
INNER JOIN dnn_Vendors ON dnn_Banners.VendorId = dnn_Vendors.VendorId
LEFT OUTER JOIN dnn_Files ON dnn_Banners.ImageFile = 'fileid=' + convert(varchar,dnn_Files.FileID)
WHERE   (dnn_Banners.BannerTypeId = @BannerTypeId or @BannerTypeId is null)
AND     (dnn_Banners.GroupName = @GroupName or @GroupName is null)
AND     ((dnn_Vendors.PortalId = @PortalId) or (@PortalId is null and dnn_Vendors.PortalId is null))
AND     dnn_Vendors.Authorized = 1
ORDER BY BannerId

GO
SET QUOTED_IDENTIFIER OFF
GO
SET ANSI_NULLS ON
GO

Thanks for the assistance,

Steve