FileUpload.PostedFile always null inside UpdatePanel

This is an old issue going way back to MSAjax 1.0 . The FileUpload control is not compatible with the way Update Panels works and the Script Manager. A file upload modifies the data stream causing the script manager to choke. The only way it will work is to have the File Upload Control outside the update panel. If you have other controls on the page that depends on the file upload control you need to set the add a PostBack trigger.

FileUpload doesn't work inside an UpdatePanel. You must use AsyncFileUpload from ASPNET AJAX control Toolkit.

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When you use AsyncFileUpload you must set the right params in the form tag, that is placed in your Page or MasterPage:

<form id="form1" runat="server" enctype="multipart/form-data" method="post">

If you don't set the right enctype and method UploadedComplete will never fire, and you won't be able to get FileUpload.FileBytes since FileUpload.HasFile returns true only during UploadedComplete execution.

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Besides, prevoius versions of AsyncFileUpload didn't work on Chrome. Actual version (4.1.50731.0) solved the problem.

You can put a FileUpload control in an UpdatePanel but you have to use a PostBackTrigger as opposed to an AsyncPostBackTrigger. I recently used this approach and combined both types of trigger.

    <Triggers>
        <asp:PostBackTrigger ControlID="btnSave" />
        <asp:AsyncPostBackTrigger ControlID="btnAsyncSave"/>
    </Triggers>

The PostBackTrigger was used for FileUploads while the AsyncPostBackTrigger was used for all the other form fields.