midlc parse error

Hello,

I get some parse error when trying to compile the idl for the net
shutdown command and am not sure if I did right.
Here are my steps so far:
- compiled midlc under cygwin
- extracted three IDL-Files from [MS-RSP].pdf (download from microsoft):
initshutdown.idl, windowsshutdown.idl winreg.idl
- executed ./midlc<filename>  for all three files

For each file I get a parse failure from midlc for line 4. This line
looks like (example from windowsshutdown.idl):
   [size_is(MaximumLength / 2), length_is((Length) / 2) ] unsigned short*
Buffer;
The corresponding lines in the other files look similar.

midlc stops in parse.c on line 69 with the message "invalid attribute".

What am I doing wrong?
Any help would be appreciated.

Thanks in advance
Robert