How to obtain the handle for a drive which is configured with enhanced write filter (ewf). The operating system is windows embedded standard

I have written a small program that do p/invoke to obtain the pointer to the EWFProtected volume or disk.

The operating system in windows embedded standard.

The c: is a protected volume. Type is RAM<REG>

When i make a function call  EwfMgrOpenProtected("C:"); return value is -1 and error value is 5 which is access denied.

How to obtain an handle to the protected volume?

static void Main(string[] args)
       {
           // HANDLE EwfMgrOpenProtected(LPCWSTR lpVolume);
           IntPtr ptr = EwfMgrOpenProtected("C:");
           int error = Marshal.GetLastWin32Error();

           Console.WriteLine("error " + error);
           Console.WriteLine(ptr);
           Console.ReadLine();
       }

       [DllImport("ewfapi.dll", SetLastError = true, CharSet = CharSet.Unicode)]
       public static extern IntPtr EwfMgrOpenProtected(string volume);