The error message detail is:
System.UnauthorizedAccessException: Access to the path "D:\inetpub\wwwroot\App_Name\resource_root\client\image\test.jpg" is denied.
...
at CuteEditor.Impl.FileSystemStorage.CreateFile(String dirpath, String filename, Byte[] filedata)
at CuteEditor.Dialogs.FileBrowserPage.uploadButton_Click(Object sender, EventArgs, e)