Cannot access parent site list from subsite in XSLt List View webpart in sharepoint designer 2010

Hi
   We are using sharepoint 2010  for internet facing sites for our big client in healthcare domain .  I am using XSLT list view webpart in sharepoint designer 2010 for retrieving contents from sharepoint list & displaying it by using XSLT List view webpart in publishing sites.

We are having lot of list in rootsite collection, If i am creating pages by using XSLt list view webpart in root site collection I can access the list,View and Display in Pages by XSLT List view webpart.

Now the requirement is i have to access the list in roosite collection(parent site) from subsites.  In Sharepoint designer 2010, while i am inserting XSLT list view webpart, i could not find datasource to access the list that exist in rootsite collection(Parent site) from subsite.

Below is the the code i am using for accessing the list& view from parent site & creating the pages in parent site by using xslt list view webpart,now i wants to access parent site list from subsite by using XSLT list view webpat in subsite pages. 

Pls let me know what i have to change in the code level

<WebPartPages:XsltListViewWebPart runat="server" Description="The list for the conditions details" ListDisplayName="" PartOrder="2" Default="FALSE" HelpLink="" AllowR

I've got an External List and I want to create a Site Column, which is Lookup to a column in my external list. If I tick any of the columns in 'Add a column to show each of these additional fields' and click OK i get the following error message:

[NullReferenceException: Object reference not set to an instance of an object.]
  Microsoft.SharePoint.SPBusinessDataField.IsInDefaultView() +58
  Microsoft.SharePoint.SPBusinessDataField.CreateSpFieldForBdcType(String bdcName, Boolean hidden, Boolean readOnly, Boolean idField, SPAddFieldOptions op) +809
  Microsoft.SharePoint.SPBusinessDataField.AddNeededSecondaryFields(String wssNames, String[] oldNames, String[] newNames, SPAddFieldOptions op) +315
  Microsoft.SharePoint.SPBusinessDataField.OnAdded(SPAddFieldOptions op) +240
  Microsoft.SharePoint.SPFieldCollection.AddFieldAsXmlInternal(String schemaXml, Boolean addToDefaultView, SPAddFieldOptions op, Boolean isMigration, Boolean fResetCTCol) +759
  Microsoft.SharePoint.SPFieldCollection.Add(SPField field) +61
  Microsoft.SharePoint.ApplicationPages.FieldNewPage.Save() +513
  Microsoft.SharePoint.ApplicationPages.FieldNewPage.BtnOk_Click(Object sender, EventArgs e) +46
  System.Web.UI.WebControls.Button.OnClick(EventArgs e) +114
  System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +139
  Syste

We have a custom list definition that includes custom site columns.  When we try to open one of the list view aspx pages in SharePoint to update the view query we get an error when trying to save the page in SharePoint Designer 2007.  We receive a warning that the operation will customize the page from the site definition, which is fine.  And then get a general "Server error: ServiceRequestorID" alert.  ServiceRequestorID is a custom site column used by the list definition.

ServiceRequestorID field definition:

<Field ID="{FA39D24D-AB40-4b1d-BD80-94ABE34A7578}" Name="ServiceRequestorID" DisplayName="Service Requestor ID" StaticName="