Comment 1 for bug 118070

I'll second this. Absolutely unable to build a Ubuntu kernel from scratch using linux-source-2.6.20_2.6.20-16.29 source package.

Damn annoying. And, yes, I'm following the fine instructions to the letter:

(copy in appropriate config from /boot)
make-kpkg clean
make-kpkg --append-to-version custom --initrd kernel_headers kernel_image modules_image

Dies with the precise error message above.