public class ChatServer extends Sprite {
public function ChatServer() {
ServerAS3SX.setRequestHandler(ChatMessage, handleChatMessageRequest);
...

// Ok
package chat.request.structure {
public class ChatMessage {
public var value : String;
public function ChatMessage(value : String = "") {
this.value = value;
}
}
}

// No response from server
package chat.request.structure {
public class ChatMessage {
public var value : String;
public function ChatMessage(value : String) {
this.value = value;
}
}
}