I\'m having this problem with GWT when it\'s behind a reverse proxy. The backend app is deployed within a context - let\'s call it /context.
The GWT app works fine
I've run into a similar problem, a successful workaround was to make all serialized objects implement GWT's IsSerializable interface (in addition to the standard Serializable interface). If you read the message, it states that 'a legacy, 1.3.3 compatible, serialization policy will be used' - the 1.3.3 compatible policy requires all of your serialized objects implement the IsSerializable interface, so by adding it, everything worked.
I do have concerns that the legacy policy will be desupported in future versions of GWT, so i am also in search for a better workaround myself.