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When you access a Microsoft ASP.NET 2.0 AJAX-enabled Web site, Web clients such as Windows Internet Explorer may have several problems. For example, the process may exit unexpectedly, or you may receive the following script error message:
Microsoft JScript runtime error: '__pendingCallbacks[...].async' is null or not an object
This problem occurs most frequently when multiple callbacks call the WebForm_CallbackComplete function at the same time. This problem occurs especially when one of the callbacks that is executed displays a modal dialog box, such as an alert dialog box or an error message.
Hotfix Replacement Information
The hotfix that corresponds to KB961864 has been superseded with the hotfix KB981201, which contains all fixes that were previously included in KB961864. You should use the hotfix KB981201 to fix the issues described in KB961864. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
981201 A hotfix is available for ASP.NET 2.0 that enables support for extended protection
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
You may receive the script error message because you are using the i global variable in the callback function. In this case, check whether you have the .NET Framework 2.0 SP2 or the .NET Framework 3.5 SP1 installed. If you do not, download and then install the service pack from one of the following Microsoft Web sites: