GWT - Unhelpful RPC serialization message

There are a number of causes for this error message:

com.google.gwt.user.client.rpc.SerializationException: Type ‘blah.blah.blah’ was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized.

Check: I have a no args constructor (private is OK)

Check: I have implemented IsSerializable

Check: It is on my source path for my module - in

What else could be wrong?

It turned out that one of the fields within my class was not Serializable due to not implementing IsSerializable.