create or inport unattend file on virtual machine. failed information.

Fail: "C:\Windows\Panther\unattend.xml" System.UnauthorizedAccessException: Access to the path 'C:\Windows\Panther\unattend.xml' is denied.
   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
   at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
   at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options, String msgPath, Boolean bFromProxy)
   at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, Boolean useAsync)
   at System.Xml.XmlWriterSettings.CreateWriter(String outputFileName)
   at System.Xml.XmlWriter.Create(String outputFileName, XmlWriterSettings settings)
   at System.Xml.Linq.XDocument.Save(String fileName, SaveOptions options)
   at System.Xml.Linq.XDocument.Save(String fileName)
   at a.A.h()