Sharpbox give an invalid URL(error 404)

Question

I'm trying to make a basic program which upload a picture into dropbox(that part is fully working) and then it give that picture public url in order to download it. I use the following code to get that url:

private void GetRessourceURI()
{
    try
    {
        ICloudDirectoryEntry fEntry = m_DropBoxStorage.GetFolder("/public");
        ICloudFileSystemEntry fs = m_DropBoxStorage.GetFileSystemObject(m_RessourceFileName, fEntry);

        m_RessourceURI = DropBoxStorageProviderTools.GetPublicObjectUrl(m_AccessToken, fs);
       // m_RessourceURI = m_DropBoxStorage.GetFileSystemObjectUrl("/" + RessourceFileName, m_DropBoxStorage.GetFolder("/"));
        Console.WriteLine(m_RessourceURI);
    }
    catch (SharpBoxException AnyException)
    {
        throw AnyException;
    }
}

when the program is running i get the following link : http://dl.dropboxusercontent.com/u/168609230/Lena.jpg , but when i want to use the link dropbox give a 404 error i tried to get the link with GetFileSystemObjectUrl but it give me a temporary URI that i cannot use. Can someone help please