I'm following the Yocto "Quick Start"[1] guide to prove the build process on my Linux PC.

My PC does not have Python 2.6 installed, so I followed the FAQ suggestion to install Python 2.6 from the Yocto external tarball[2].

At build time I get the following:

[parkint1@crow build]$ bitbake poky-image-sato
Pseudo is not present but is required, building this first before the main build
Traceback (most recent call last):
  File "/home2/parkint1/src/yocto/poky-bernard-5.0/bitbake/bin/bitbake", line 39, in <module>
    from bb import cooker
  File "/home2/parkint1/src/yocto/poky-bernard-5.0/bitbake/lib/bb/cooker.py", line 30, in <module>
    import multiprocessing
ImportError: No module named multiprocessing

I followed the same Quick Start process on a PC with Python 2.6, using my PC's installed version of Python rather than the external tarball.  This ran fine.

[1]. http://www.yoctoproject.org/docs/yocto-quick-start/yocto-project-qs.html
[2]. http://www.yoctoproject.org/docs/poky-ref-manual/poky-ref-manual.html#id2764616