linq query for lookup list column error - query uses unsupported elements

I'm trying to return the list item ID (s.ID), and the ID of a lookup column (s.VendorID). I get the following error:

The query uses unsupported elements, such as references to more than one list, or the projection of a complete entity by using EntityRef/EntitySet.

Is this error because s.VendorID is from a lookup column? (Edit: This does seem to be related to the lookup column. I can return data from more than one non-lookup column in the table. However, I need the lookup column so that adding list items works for end users.)

How can I get this to work? Code examples appreciated.

using (SPLinqDataContext dc = new SPLinqDataContext(SPContext.Current.Web.Url))
{
    {
        EntityList<VendorSearchesItem> vendorSearches = dc.GetList<VendorSearchesItem>("Vendor Searches");

        var vendorSearchesQuery = from s in vendorSearches
                                  select new
                                  {
                                      s.Id,
                                      s.VendorID //lookup column
                                  };

        spGridView.DataSource = vendorSearchesQuery; 
        spGridView.DataBind();
    }
}