I've encountered a problem recently. The MIDI library has problems with xml serialization. Is does not support it.
Use the N-Audio libraries in a diffrent class than your object you want to serialize.
Example:--> Class 1(data) =ordinary data types like struct, int, string, etc. ***you'll be able to serialize this class***
Class 2 (N-Audio) = Methods with midiplayer, N-audio types, Static methods to construct the midiEvent collections **Do not serialize
Hope this helps :)