Such error is commonly displayed if one of the following settings is not set:
- check if the value set in the TargetPhysicalFolder property of the Upload control really exists on your server.
- check if you have allowed writing to the virtual folder.
- check if the default user connected to the virtual folder have permissions to add/remove files in that directory.
In case none of the above steps helped, could you please send us a sample project so we could see the settings in your web project and xaml definition.
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