WebPart Connections on Sharepoint. - Which type to use?

I wrote a sample webpart that takes a parameter passed from the orher webpage and displays its value on a label. Here is the code:

[Guid("11a885e9-13e1-4c6e-8045-e5575794ebd8")]
public class DisplayParameter : System.Web.UI.WebControls.WebParts.WebPart
{
    protected Label _label = new Label();
    private string _message; 

    [ConnectionConsumer("Parameter to show")]
    public void GetWPConnectedProviderInterface(IWebPartField connectProvider)
    {
        FieldCallback callback = FieldCallback;
        connectProvider.GetFieldValue(callback);
    }

    private void FieldCallback(object fieldValue)
    {
        _message = (string)fieldValue;
    }

    protected override void OnPreRender(EventArgs args)
    {
        if (string.IsNullOrEmpty(_message))
            _label.Text = "No Message.";
        else
            _label.Text = _message;
    }

    protected override void CreateChildControls()
    {
        base.CreateChildControls();
        Controls.Add(_label);
    }
}

      

        
        
        
      

    

Then I put WP on the page and WP DataView generated with SPD to pass the filename from the Doc library to WP.
It works fine the first time, but when I select another document, I get the following exception:

Cannot pass object of type 'Test.Assembly.SharepointProject.DislayParameter' for input 'Microsoft.SharePoint.WebPartPages.WebPart'.

This makes me think ... Should I inherit from Microsoft.SharePoint.WebPartPages.WebPart instead of System.Web.UI.WebControls.WebParts.WebPart ?, and if so, what are the disadvantages of doing this since MSDN and bloggers suggest using the latter class?