See [this code](https://github.com/protegeproject/webprotege-gwt-api-gateway/blob/9a7fbb923934717e56c7820fb5f6760184682fc2/src/main/java/edu/stanford/protege/webprotege/gateway/RpcRequestProcessor.java#L78). Logging should be added here and if possible a more descriptive error code should be returned.