MARS Issue With Typed DataSets?

I have a DAL that uses Typed DataSets (not directly, the DAL references and calls the dataset methods) and I am receiving a "There is already an open DataReader associated with this Command which must be closed first." error when I render an ASP.NET page where two imgs need to retrieve two different versions of an image (a thumbnail and a full sized image).
I am using SQL Server 2005, ASP.NET 2.0, and my connection string includes the MARS attribute set to true. 
 
This is the method in the SqlServer DAL, _images is a typed table adapter:
public override Image SelectImage(Guid? id)
    {
        // TODO: Find out why MARS feature isn't working!
        DataSet.ImageDataTable dt = _images.SelectImageById(id); <-- Exception occurs here
        if ((dt != null) && dt.Count == 1)
        {
            DataSet.ImageRow row = dt[0];
            Guid? keyId = null;
            if (!row.IsKeyIdNull())
            {
                keyId = row.KeyId;
            }

            // Success
            return new Image(row.Id, keyId, row.Path, row.Caption);
        }
        return null;
    }
 
// This is the method that is called for both images, which calls the DAL
public class EntitySearch
{
    public static Image ImageById(Guid id)
    {
        return _dal.SelectImage(id);
    }
}

// These are the code-behind methods that the image response strings will come from...
imgThumbnail.ImageUrl = String.Format("../Services/ImageBroker.aspx?img={0}&mode=Thumbnail", image.Id);
imgFullImage.ImageUrl = String.Format("../Services/ImageBroker.aspx?img={0}&mode=Image", image.Id);
           
// And finally here is the code in the broker class that saves the images to the response stream
Image image = EntitySearch.ImageById(imageId);
using (Picture picture = (mode == ImageMode.Image) ? image.Picture : image.Thumbnail)
{
    Picture.Save(response.OutputStream, ImageFormat.Jpeg);
}
So the final snippet of code is being called twice, and it crashes. I have tried closing the connection and reopening it as a workaround but this only yields strange results, though it intermittently does load the images.
Can anyone spot the issue?