Matplotlib *egg* gives error about trying to modify system files...

I'm trying to install the matplotlib egg on Debian Etch.
I got g++, pygtk and everything else I could think that matplotlib
wants. It froze with following mysterious message...

The package setup script has attempted to modify files on your system
that are not within the EasyInstall build area, and has been aborted.

This package cannot be safely installed by EasyInstall, and may not
support alternate installation locations even if you run its setup
script by hand. Please inform the package's author and the EasyInstall
maintainers to find out if a fix or workaround is available.