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PO.NET error when calling System.Net.WebClient.UploadFileAsync
 

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    <p>I am working with the <code>System.Net.WebClient</code> class, and I am attempting to upload a file using the UploadFileAsync method. I am using Visual Studio 2010, and all of my projects are set to use the .NET 4.0 standard runtime, not the client library.</p> <p>Below is a small section of the code that I am using. About 90% of the time I get the following error:</p> <p><strong>Unable to cast object of type 'System.ComponentModel.AsyncOperation' to type 'UploadBitsState'.</strong></p> <pre><code>Stack Trace: at System.Net.WebClient.UploadFileAsyncWriteCallback(Byte[] returnBytes, Exception exception, Object state) at System.Net.WebClient.UploadFileAsync(Uri address, String method, String fileName, Object userToken) at FileUpload._StartUpload() </code></pre> <p>The FTP servers I am attempting to upload to are internal to my organization, but one is running IPSwitches WS-FTP and the other is running an IIS 6.0 FTP site, and I have experienced the same issue with both servers.</p> <p>I have searched high and low for others with a similar problem to no avail.</p> <p>The actual line that the exception occurs on is the <code>_Client.UploadFileAsync</code> method call.</p> <pre><code>private void _StartUpload() { try { _Client = new WebClient { Credentials = _Credentials }; _Client.UploadProgressChanged += ProgressChanged; _Client.UploadFileCompleted += UploadCompleted; _Client.UploadFileAsync(FileBeingUploaded, "STOR", _LocalFile, null); } catch (Exception exception) { // Methods calls removed for brevity } } private void UploadCompleted(Object sender, UploadFileCompletedEventArgs e) { // Methods calls removed for brevity } private void ProgressChanged(object sender, UploadProgressChangedEventArgs e) { // Methods calls removed for brevity } </code></pre>
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    1. USPeter Mortensen
    1. USDale Couch
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    1. CODoes it work when you execute it synchronously? Have you tried watching the traffic with a packet sniffer such as `tcpdump` or `WireShark`?
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      1. USRyan Emerle
    2. COI have not tried a synchronous call. As for a sniffer, I have not tried to watch these specific errors, but given that the exception is within the .Net framework and it is a cast issue, I am not sure what the TCP traffic analysis would show.
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      1. USDale Couch
    3. COIs the file you are uploading `_LocalFile` a static file? In other words, is there **any** possibility of the content of the file being modified/updated while being uploaded? I ask because I can duplicate your error in that particular scenario.
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