异步线程在SharePoint Web部件中消失

I wrote a custom web part for SharePoint 2007 that loads an existing user control. One of the things the user control does is an asynchronous upload of a file via FTP. I'm using a third-party FTP library that has BeginUpload/EndUpload methods for async file transfer. I also have an update panel in the user control that I use to display a running total of the number of bytes that have been transferred, based on an event raised by the FTP library. I've added all the necessary AJAX settings to web.config.I wrote a custom web part for SharePoint 2007 t