Accepting new tags (user defined) in responce

I have defined a new user defined tag by extending StringField class, as defined in the documentation.

Now I am able to send this tag/value pair by using setField method. Problem is when I get the same tag in response the message is being rejected at server level.

Do I need to add the same in DataDictionary also OR is there another way.

Thanx a ton
Ashish