Best success so far. Retrieves counts for both Artefacts and Drives queryables. Only crashes when I try to use a query that uses a FirstOrDefault() with a lambda expression as the argument. If I'm lucky though, this is only because when it invokes ClientQueryProvider.Execute() it tries to pass the expression using a BinaryFormatter. Try changing it to use Serialize.Linq.ExpressionNode instead, which is what ClientQueryProvider.CreateQuery() does