[DllImport("ole32.dll", ExactSpelling=true, PreserveSig=false)]
static extern int CoCreateGuid ( out Guid guid );
None.
While debugging in VS, you may get an error. Disable the error, and the code runs just fine.
If you like the old-style GUIDs that are generated in sequential order and contain the machine's MAC address, try UuidCreateSequential.
Guid guid;
CoCreateGuid ( out guid );
string guid_s = guid.ToString();
// or:
Marshal.ThrowExceptionForHR ( CoCreateGuid ( out guid ) , new IntPtr ( -1 ) );
guid_s = guid.ToString();
System.Guid.NewGuid()