Help with BsonClassMap.RegisterClassMap

I am using c#. I have a class GeoCoordinates which just has this 2 variables lat, lon
I also have an array of GeoCordinates
Previously I was able to register a class map as follows
I am migrating to c# driver 2.19. The mapping GeoCoordinates is failing and I get an error, unable to deserialize object.
Is there a different way of registering array of objects? Any help will be appreciated