grep: /usr/src/linux/include/linux/autoconf.h: No such file or directory
make -C /usr/src/linux SUBDIRS=/usr/src/asterisk/zaptel-1.4.0 modules
make[1]: Entering directory `/usr/src/linux-headers-2.6.18-3'
Makefile:266: /usr/src/linux-headers-2.6.18-3/scripts/Kbuild.include: No such file or directory
/bin/sh: line 0: [: -lt: unary operator expected

  ERROR: Kernel configuration is invalid.
         include/linux/autoconf.h or include/config/auto.conf are missing.
         Run 'make oldconfig && make prepare' on kernel src to fix it.

make[1]: *** No rule to make target `/usr/src/linux-headers-2.6.18-3/scripts/Kbuild.include'.  Stop.
make[1]: Leaving directory `/usr/src/linux-headers-2.6.18-3'
make: *** [linux26] Error 2