Optimize Linq To SQL Query, Group By Multiple Fields

My LINQ query contains the following Group By statement:

Group p By Key = New With { _
.Latitude = p.Address.GeoLocations.FirstOrDefault(Function(g) New String() {"ADDRESS", "POINT"}.Contains(g.Granularity)).Latitude, _
.Longitude = p.Address.GeoLocations.FirstOrDefault(Function(g) New String() {"ADDRESS", "POINT"}.Contains(g.Granularity)).Longitude}

The query works, but here is the SQL that the clause above produces

SELECT [t6].[Latitude]
FROM (
SELECT TOP (1) [t5].[Latitude]

[Code]....

but this produced an error: "A group by expression can only contain non-constant scalars that are comparable by the server."