Raised when an error occurs on the server. If an error occurs on the server while the request is being processed, an error response is returned to the browser and the Sys.WebForms.PageRequestManagerServerErrorException exception is raised. To customize error handling and to display more information about the server error, handle the AsyncPostBackError event and use the AsyncPostBackErrorMessage and AllowCustomErrorsRedirect properties. For an example of how to provide custom error handling during partial-page updates, see Customizing Error Handling for ASP.NET UpdatePanel Controls.