Similarly as with multiple-element operations (above), errors in subscriptions are reported to your code by means of an Exception property in the event arguments passed to your event handler or callback method. If this exception is a null reference, then there has been no error related to the event notification, and other data contained in the event arguments object is valid. When the exception is not a null reference, it contains the actual error.

In event notifications, the exceptions are not wrapped in OpcException or UAException, because there is no need for you to distinguish them from other exception types in the catch statement. If there is an exception related to the event notification, it is always an exception related to OPC operations.