I kept getting this error and I solved it by editing Dm-target.c and going to line 659 and removing the last NULL in the function parameters list. Apparently someone in the kernel sphere modified the params list and then changed it back; here's the background info
http://lkml.org/lkml/2007/7/29/187. After running build.sh it worked fine.
Checking build requirements...
Building kernel module... /root/software/src/truecrypt-4.3a-source-code/Linux/Kernel/Dm-target.c: In function ‘dm_truecrypt_init’:
/root/software/src/truecrypt-4.3a-source-code/Linux/Kernel/Dm-target.c:659: error: too many arguments to function ‘kmem_cache_create’
make[2]: *** [/root/software/src/truecrypt-4.3a-source-code/Linux/Kernel/Dm-target.o] Error 1
make[1]: *** [_module_/root/software/src/truecrypt-4.3a-source-code/Linux/Kernel] Error 2
make: *** [truecrypt] Error 2
Error: Failed to build kernel module