Asp.net cannot calculate the expression value because the code has been optimized or the local framework is located on the call stack.

Look at the solution given by MS: (http://support.microsoft.com/kb/312629)

Symptoms:
If you use the Response. End, Response. Redirect, or Server. Transfer method, a ThreadAbortException exception occurs. You can use the try-catch statement to catch this exception.
Cause:
The Response. End method terminates the page execution and switches this execution to the Application_EndRequest event in the event pipeline of the application. Do not execute the code line after Response. End.

This problem occurs in the Response. Redirect and Server. Transfer methods, because both methods call Response. End internally.
Solution:
To solve this problem, use one of the following methods:

For Response. Redirect, use the overload Response. Redirect (String url, bool endResponse). This overload will pass false to the endResponse parameter to cancel internal calls to Response. End. For example:
Response. Redirect ("nextpage. aspx", false); if this alternative method is used, the Code following Response. Redirect is executed.
For Server. Transfer, use the Server. Execute method.
Change the code to Response. Redirect (str, false );

Solve the problem.

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Call data in Ext
Response. Clear ();
Response. Write (sMessage );
HttpContext. Current. ApplicationInstance. CompleteRequest ();
// Response. End ();