I've googled this a bit, and didn't really find anything for it.
Not really sure what to do here...
(I'm running Damn Small Linux, if that's of any help)

dsl@box:~/gaim-0.80$ ./configure
checking build system type... i586-pc-linux-gnulibc1
checking host system type... i586-pc-linux-gnulibc1
checking target system type... i586-pc-linux-gnulibc1
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for gawk... no
checking for mawk... mawk
checking whether make sets $(MAKE)... no
checking for sed... /bin/sed
checking for gcc... gcc
checking for C compiler default output file name... a.out
checking whether the C compiler works... yes
checking whether we are cross compiling... no
checking for suffix of executables...
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ANSI C... none needed
checking for style of include used by make... none
checking dependency style of gcc... none
checking for a sed that does not truncate output... /bin/sed
checking for egrep... grep -E
checking for ld used by gcc... /usr/bin/ld
checking if the linker (/usr/bin/ld) is GNU ld... yes
checking for /usr/bin/ld option to reload object files... -r
checking for BSD-compatible nm... /usr/bin/nm -B
checking whether ln -s works... yes
checking how to recognise dependent libraries... pass_all
checking how to run the C preprocessor... /lib/cpp
configure: error: C preprocessor "/lib/cpp" fails sanity check
See `config.log' for more details.
dsl@box:~/gaim-0.80$

From Lunar Linux.org

Q: configure: error: C preprocessor "/lib/cpp" fails sanity check ?
Submitted by nestu on Thu, 05/20/2004 - 14:27.

Your kernel headers are missing from /usr/include. This means the C PreProcessor cannot verify that it has the proper cached copies of those vital header files. You need to install the proper ones manually. Here's how:

1. might work for you!

2. Otherwise:
to create the two target dirs, if needed. Then execute:
to copy the files manually. Be warned that the second command has to be done this way since /usr/src/linux/include/asm is a softlink to your arch asm header files (asm points to asm-i386, on x86 machines). So if, on the other hand, you had copied

you would then get a softlink to nowhere under /usr/include/.

3. Last, you can always try to unpack the kernel tarball you have into /usr/src/linux and manaully link or copy the headers over yourself.

Man ty so much. I am such a noob. I had kernel 2.4 installed and the source in /usr/src/linux

Last night i recompiled to kernel 2.6.81 and the source of that one was in /usr/src/linux-2.6.8.1

I went and deleted the dir linux without ermakign a sympbolic link hehe or atleast rename the source of the new kernel.

Then today I tried to compile somethig ans it gave me that error that /lib/cpp didnt pass sanity check. I treid to install gcc 3.4 and atleast 25 other things before i gave up and asked my best buddy google.

And here was your post. hehe so simple but man linux doesnt forgive. Next time ill read the fuckn manual

Thanks buddy