using System;
using System.Runtime.Serialization;

throw new SimpleException(); //<- Error

throw new RecommendExc("exeption"); //<- Error

class SimpleException: Exception { }

class RecommendExc: Exception {
    //recommended constructors
    public RecommendExc () { }
    public RecommendExc(string message) : base( message ) { } 
    public RecommendExc(string message, Exception inner) : base ( message,
                          inner ) { }
    protected RecommendExc(SerializationInfo info,
                          StreamingContext context): base ( info, context ) { }

    //... any other members
}