make problem with simple IDL target

Hi,
   I'm trying to build a trivial makefile.win for a trivial component.

I have a single .IDL file, and want to create and install the 
type-library.  My makefile.win is:

8< 8< 8<
DEPTH   =..\..\..\..\..
MODULE=pyxpcom

XPIDLSRCS = .\py_test_component.idl \
	$(NULL)

include <$(DEPTH)\config\rules.mak>
8< 8< 8<

It seems to build and run fine.  However, if I attempt a second make 
immediately after the (successful) first, I get:

8< 8< 8<
+++ make: exporting IDL files
+++ make: exporting generated XPIDL header files
perl.exe -I..\..\..\..\..\config ..\..\..\..\..\config\build-list.pl 
..\..\..\..\..\dist\i
nclude\pyxpcom/.headerlist .\_xpidlgen\py_test_component.h
Can't find unicode character property definition via main->y or y.pl at 
unicode/Is/y.pl li
ne 0
NMAKE : fatal error U1077: 'perl.exe' : return code '0xff'
8< 8< 8<

If I remove the mozilla/dist/include/pyxpcom directory, then the build 
will again succeed.  However, the next build with again fail with the 
same error.

I can't see why this is happening, or how this makefile differs from 
other makefiles in the tree that obviously work.  My makefile seems 
almost identical to other ones in the tree - eg, 
http://lxr.mozilla.org/seamonkey/source/extensions/transformiix/public/makefile.win

Is it necessary for module names to be defined somewhere?  I can't find 
it!  Anyone have any other clues what is going wrong?

Thanks,

Mark.