How to extend AMessage to create sub messages for sub fields OpenIso8583.Net

Question

I am using OpenIso8583.Net to generate my ISO messages and everything is perfect except I am having troubles generating a message for a sub field.

I know I have to extend the AMessage class to achieve but clearly I am going about it all wrong.

Any simple example will help a lot. I would paste code but I am so far it's useless I am hoping this post makes sense to someone who has worked with sub fields on the ISO 8583 spec

http://code.google.com/p/openiso8583net/ above is the link to the library I am using

thanks