Sometimes when running Exchange Toolbox I'll get a Snap-in Unavailable message. Specifically:
This snap-in performed a non-valid operation and has been unloaded. To continue working with this snap-in, restart MMC or try load the snap-in again.
Exception Type: System.Runtime.Serialization.SerializationException
Exception Message: Type is not resolved for member.
The problem usually has to do with IIS. Open IIS Manager, expand the 'Sites' folder in the left menu. In the right Actions pane, select 'Bindings...'. The bindings have to be like this screenshot (via Spiceworks), specifically the binding needs to include HTTP to all assigned IPs at port 80 and HTTPS at port 443.
If that is already set, a restart of IIS has helped.
