Typically, when a callback sent by a web control is processed on the server side and an unhandled server error occurs, the web application becomes unresponsive to the end-user (i.e., it crashes or hangs in the client's browser). DevExpress ASP.NET controls implement a built-in callback error-handling mechanism, which enables a web application to remain responsive in this case.
The ASPxHttpHandlerModule provides this error-handling mechanism, which catches unhandled server exceptions that occur during callback processing. The module generates and sends a specific response that contains exception-related information, to prevent the application from remaining in an unresponsive state.
By default, error messages are displayed within a browser based on the callback initiator (a DevExpress web control or an external control). An AJAX-enabled DevExpress web control shows error information within its embedded UI element, whereas an external control displays error details within a popup message box.
The error message content to be sent to remote clients depends on the customErrors mode setting defined in web.config. Before the message is sent to a client, you can modify it with a DevExpress API. See the following topic to learn more: