freebsd stable - Dec 2007 - amsn-0.96_1 does not build

amsn-0.96_1 does not build because of the following error:

===>  Building for amsn-0.96_1
  CXX     utils/TkCximage/src/TkCximage.cpp.o
In file included from utils/TkCximage/src/TkCximage.cpp:11:
utils/TkCximage/src/TkCximage.h:23:25: tkPlatDecls.h: No such file or directory
gmake: *** [utils/TkCximage/src/TkCximage.cpp.o] Error 1
*** Error code 2

Stop in /usr/ports/net-im/amsn.
==

My ports tree is up to date (portsnap fetch and update alright).

Any idea why this header file is missing ?

Thank you in advance for any help.

HW
-- 
FreeBSD 6.2-RELEASE-p2 #0: Tue Feb 27 22:56:09 UTC 2007