Q:

Saving a file to 'C:\Windows\System32\dns' causes 'Could not find a part of the path' error

I've written a windows forms (.net 4) application that needs to write a file to the folder 'C:\Windows\System32\dns'.  When this line of code runs:
File. WriteAllText(dnsFileLocation, luxDns)

I get the following error, does anyone know why? 
Note: This happens even if I run the application as administrator! 
***** Exception Text *******
System. IO.DirectoryNotFoundException: Could not find a part of the path 'C:\Windows\System32\dns\lux2.dns'. 
   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)
   at System. IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options)
   at System. IO.StreamWriter. CreateFile(String path, Boolean append)
   at System. IO.StreamWriter..ctor(String path, Boolean append, Encoding encoding, Int32 bufferSize)
   at System. IO.StreamWriter..ctor(String path, Boolean append, Encoding encoding)
   at System. IO.File. InternalWriteAllText(String path, String contents, Encoding encoding)
   at System. IO.File. WriteAllText(String path, String contents)
   at DnsServerUpdater. Main. Main_Load(Object sender, EventArgs e)
   at System. EventHandler. Invoke(Object sender, EventArgs e)
   at System. Windows. Forms. Form. OnLoad(EventArgs e)
   at System. Windows. Forms. Form. OnCreateControl()
   at System. Windows. Forms. Control. CreateControl(Boolean fIgnoreVisible)
   at System. Windows. Forms. Control. CreateControl()
   at System. Windows. Forms. Control. WmShowWindow(Message& m)
   at System. Windows. Forms. Control. WndProc(Message& m)
   at System. Windows. Forms. ScrollableControl. WndProc(Message& m)
   at System. Windows. Forms. Form. WmShowWindow(Message& m)
   at System. Windows. Forms. Form. WndProc(Message& m)
   at System. Windows. Forms. Control. ControlNativeWindow. OnMessage(Message& m)
   at System. Windows. Forms. Control. ControlNativeWindow. WndProc(Message& m)
   at System. Windows. Forms. NativeWindow. Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

************** Loaded Assemblies **************
mscorlib
    Assembly Version: 4.0.0.0
    Win32 Version: 4.0.30319.261 (RTMGDR.030319-2600)
    CodeBase: file:///C:/Windows/Microsoft. NET/Framework/v4.0.30319/mscorlib.dll
----------------------------------------
DnsServerUpdater
    Assembly Version: 1.0.0.0
    Win32 Version: 1.0.0.0
    CodeBase: file:///C:/web/dns/DnsServerUpdater.exe
----------------------------------------
Microsoft. VisualBasic
    Assembly Version: 10.0.0.0
    Win32 Version: 10.0.30319.1 built by: RTMRel
    CodeBase: file:///C:/Windows/Microsoft. Net/assembly/GAC_MSIL/Microsoft. VisualBasic/v4.0_10.0.0.0__b03f5f7f11d50a3a/Microsoft. VisualBasic.dll
----------------------------------------
System
    Assembly Version: 4.0.0.0
    Win32 Version: 4.0.30319.261 built by: RTMGDR
    CodeBase: file:///C:/Windows/Microsoft. Net/assembly/GAC_MSIL/System/v4.0_4.0.0.0__b77a5c561934e089/System.dll
----------------------------------------
System. Core
    Assembly Version: 4.0.0.0
    Win32 Version: 4.0.30319.233 built by: RTMGDR
    CodeBase: file:///C:/Windows/Microsoft. Net/assembly/GAC_MSIL/System. Core/v4.0_4.0.0.0__b77a5c561934e089/System. Core.dll
----------------------------------------
System. Windows. Forms
    Assembly Version: 4.0.0.0
    Win32 Version: 4.0.30319.235 built by: RTMGDR
    CodeBase: file:///C:/Windows/Microsoft. Net/assembly/GAC_MSIL/System. Windows. Forms/v4.0_4.0.0.0__b77a5c561934e089/System. Windows. Forms.dll
----------------------------------------
System. Drawing
    Assembly Version: 4.0.0.0
    Win32 Version: 4.0.30319.276 built by: RTMGDR
    CodeBase: file:///C:/Windows/Microsoft. Net/assembly/GAC_MSIL/System. Drawing/v4.0_4.0.0.0__b03f5f7f11d50a3a/System. Drawing.dll
----------------------------------------
System. Runtime. Remoting
    Assembly Version: 4.0.0.0
    Win32 Version: 4.0.30319.1 (RTMRel.030319-0100)
    CodeBase: file:///C:/Windows/Microsoft. Net/assembly/GAC_MSIL/System. Runtime. Remoting/v4.0_4.0.0.0__b77a5c561934e089/System. Runtime. Remoting.dll

***** JIT Debugging *******
To enable just-in-time (JIT) debugging, the .config file for this
application or computer (machine.config) must have the
jitDebugging value set in the system.windows.forms section. 
The application must also be compiled with debugging
enabled. 
For example:
<configuration>
    <system.windows.forms jitDebugging="true" />
</configuration>

When JIT debugging is enabled, any unhandled exception
will be sent to the JIT debugger registered on the computer
rather than be handled by this dialog box. 

A:

Are you running 64bit windows ?  If yes then that's probably your issue as you will get redirected in another directory. 
You will need to implement
http://msdn.microsoft.com/en-us/library/windows/desktop/aa365743%28v=vs.85%29.aspx and 
http://msdn.microsoft.com/en-us/library/windows/desktop/aa365745%28v=vs.85%29.aspx
in order to temporarily disable the 64bit redirection in order to access that folder.