This is the base class for COM interop and SEH (Structured Exception Handler) exceptions.

public class ExternalException : SystemException {
// Public Constructors
   public ExternalException( );
   public ExternalException(string message);
   public ExternalException(string message, Exception inner);
   public ExternalException(string message, int errorCode);
// Protected Constructors
   protected ExternalException(System.Runtime.Serialization.SerializationInfo info,
       System.Runtime.Serialization.StreamingContext context);
// Public Instance Properties
   public virtual int ErrorCode{get; }
}

Hierarchy

System.Object System.Exception(System.Runtime.Serialization.ISerializable) System.SystemException ExternalException

Subclasses

COMException, SEHException