Troubleshooting Inherited Event Handlers in Visual Basic
This topic lists common issues that arise with event handlers in inherited components.
Code in Event Handler Executes Twice for Every Call
An inherited event handler must not include a Handles Clause (Visual Basic) clause. The method in the base class is already associated with the event and will fire accordingly. Remove the Handles clause from the inherited method.
If the inherited method does not have a Handles keyword, verify that your code does not contain an extra AddHandler Statement or any additional methods that handle the same event.