FileUpload multi caricamento

[Dario the best]

ho seguito l'esempio:

<script type="text/javascript">
function onFileUploadComplete(s, e) {
if (e.callbackData) {
var fileData = e.callbackData.split('|');
var fileName = fileData[0],
fileUrl = fileData[1],
fileSize = fileData[2];
DXUploadedFilesContainer.AddFile(fileName, fileUrl, fileSize);
}
}
</script>

<dx:ASPxUploadControl ID="Fileup" runat="server" ClientInstanceName="UploadControl" Width="320"
NullText="Select multiple files..." UploadMode="Advanced" ShowUploadButton="True" ShowProgressPanel="True"
OnFileUploadComplete="UploadControl_FileUploadComp lete">
<AdvancedModeSettings EnableMultiSelect="True" EnableFileList="True" EnableDragAndDrop="True" />
<ValidationSettings MaxFileSize="4194304" AllowedFileExtensions=".jpg,.jpeg,.gif,.png">
</ValidationSettings>
<ClientSideEvents FileUploadStart="function(s, e) { DXUploadedFilesContainer.Clear(); }"
FileUploadComplete="onFileUploadComplete" />
</dx:ASPxUploadControl>

mi esce il seguente errore: Unknown server tag 'dx:ASPxUploadControl'.
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