namespace System
{
public class Exception : ISerializable, _Exception
{
}
}
1.you can not create a partial class of Exception becoz Exception is not a partial
2.Your Exception class means your_projectname.System.Exception which is not equals to System.Exception
3.All partial-type definitions meant to be parts of the same type must be defined in the same assembly and the same module (.exe or .dll file). Partial definitions cannot span multiple modules.