I am using Master Page. I upgraded the AJAX control toolkit to 4.1.60623 (6 25 2012).
The OnUploadComplete event handler for ajaxfileupload does not edit the server control on the page like label, textbox, neither could it modify the viewstate variable of the page. It seems to me that this server function does not do postback of any kind.
This could trigger the postback, and, using some hidden fields, I could manage to resolve the difficulty.
But I am admiring if there is some simpler way to let the OnUploadComplete event handler run the server code and update the server control directly