Thursday, July 16, 2009

Tip - Silverlight's AsyncCallbackException on invoking WCF service

A Silverlight application deployed to the testserver gave a browser error upon invoking a WCF service. This WCF service is running on the same testserver. The error message is:
Error: Unhandled exception in Silverlight2 application [AsyncCallbackException]
According to the callstack, the error occurred somewhere in the completion of the asynchronous WCF call. This makes the bug analysis somewhat trickier, since you cannot simple use System.Windows.Browser.HtmlPage.Window.Alert then. The call completion namely does not run at the UI thread. However, searching around gave me an idea of the problem cause: I forgot to deploy a clientaccesspolicy.xml file within the folder of the deployed WCF service. Copied it there, and the call from the Silverlight client executes successfully.

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