Group and sort LINQ, c# asp

spGetData PROC returns few fields. The code below attempts to sort each separately before putting them in their respective list boxes. I have 2 errors:

Line 5 in this code: .OrderBy(getField2) has the following error:
'System.Data.Linq.ISingleResult<spGetDataResult>' does not contain a definition for 'OrderBy' and the best extension method overload 'System.Linq.Queryable.OrderBy<TSource,TKey>(System.Linq.IQueryable<TSource>, System.Linq.Expressions.Expression<System.Func<TSource,TKey>>)' has some invalid arguments      


Line 5 again: .OrderBy(getField2)
Instance argument: cannot convert from 'System.Data.Linq.ISingleResult<spGetDataResult>' to 'System.Linq.IQueryable<spGetDataResult>'      

Question: How can I correct these two errors?

A working sample using a table instead of a stored procedure included below for your inspection. This sample does exactly the same task but using a table.

               lb.Items.Clear();
               ParameterExpression o = Expression.Parameter(typeof(spGetDataResult));
               var getField2 = Expression.Lambda<Func<spGetDataResult, string>>(Expression.Property(o, fieldName), o);
               ListItem[] my_outputs = (wscgsContext.spGetData("Mike");
                                    .OrderBy(getField2)
                                    .GroupBy(getField2)
                                    .Select(theGroup => theGroup.FirstOrDefault())
                                    .Select(getField2)
                                    .Select(field => new ListItem(field))).ToArray();
               lb.Items.AddRange(my_outputs);

// The sample code below does the same thing successfully using table called Serach vs a PROC above:
private void LoadListBoxes(ListBox lb)
    {
           lb.Items.Clear();
           string fieldName = lb.ID.Substring(3);

               ParameterExpression o = Expression.Parameter(typeof(Search));
               var getField = Expression.Lambda<Func<Search, string>>(Expression.Property(o, fieldName), o);
               ListItem[] outputs = (wscgsContext.Searches
                                    .OrderBy(getField)
                                    .GroupBy(getField)
                                    .Select(theGroup => theGroup.FirstOrDefault())
                                    .Select(getField)
                                    .Select(field => new ListItem(field))).ToArray();
               lb.Items.AddRange(outputs);
}

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