[ns] makefile error during recompiling ns new modules

["Padovani, Fabrizio" <pado@libero.it>]

Hi,
I need to add new protocols to ns, so I read the tutorial and did what it
explains about that (see Ch. VII).
I copied modified files: agent.cc, agent.h; ip.cc, ip.h; packet.cc,
packet.h;
and the new files: SlotDiffEF.cc, SlotDiffEF.h; SlotDiffAF.cc,
SlotDiffEF.h; optdiff-TCP.cc, optdiff-TCP.h;
in the 'ns-2.1b8a' directory, then I edited 'Makefile.in' to add the
.o new files as I read in the tutorial,
then I did 'make depend' and it told me that 'Makefile.in' in newer and
to run 'configure', so I did and then
I did 'make' but received this error:

Makefile:139: *** commands commence before first target. 
Stop.
Ns make failed!

where 139 is the line where I put the .o new files to be added.
What kind of error is this and how can I resolve that problem?
Thanx
P.S. Sorry for my english, I'm italian and not so fluent with english
(and ns...) as I would be...