[cologsx]

I did exactly what you did but I'm still unable to install.

uname -r
2.6.25.5-1.1-default

Making module
make -C /lib/modules/2.6.25.5-1.1-default/build SUBDIRS=/tmp/vpnclient modules
make[1]: Entering directory `/usr/src/linux-2.6.25.5-1.1-obj/x86_64/default'
make -C /usr/src/linux-2.6.25.5-1.1 O=/usr/src/linux-2.6.25.5-1.1-obj/x86_64/default/. modules
/usr/src/linux-2.6.25.5-1.1/scripts/Makefile.build:46: *** CFLAGS was changed in "/tmp/vpnclient/Makefile". Fix it to use EXTRA_CFLAGS. Stop.
make[3]: *** [_module_/tmp/vpnclient] Error 2
make[2]: *** [sub-make] Error 2
make[1]: *** [all] Error 2
make[1]: Leaving directory `/usr/src/linux-2.6.25.5-1.1-obj/x86_64/default'
make: *** [default] Error 2
Failed to make module "cisco_ipsec.ko".

Any thoughts?