Assembly: BioSharp.Core (in BioSharp.Core.dll) Version: 0.1.3191.26120 (0.1.0.0)
public class IllegalSymbolException : BioException
The usual reason for throwing an IllegalSymbolException is that you are trying to add a symbol to a sequence with an alpabet that does not contain the symbol. This is the sequence/alphabet equivalent of a ClassCastException for objects.
Frequently, these excepions are actualy generated from Alphabet.validate.
Original BioJava version by Matthew Pocock. Port to C# by Doug Swisher.