passA partial-page update is initiated by a client request (an asynchronous postback) to the server. The server processes the request and returns a response to the client.
If the browser does not receive a response in a specified time, the Sys.WebForms.PageRequestManagerTimeoutException is raised. To change the interval that elapses before asynchronous postbacks time out, set the AsyncPostBackTimeout property of the ScriptManager control.
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 UpdatePanel Controls.
If the response to an asynchronous postback returns without an error but there is an error processing the response in the client, the Sys.WebForms.PageRequestManagerParserErrorException is raised. For information about how to handle this error condition, see ASP.NET AJAX Debugging and Tracing Overview.
How to avoid this problem:
1. Calls to Response.Write():