I tried to install scikit-learn on my Linux Mint 12 but failed. I downloaded the package from http://pypi.python.org/pypi/scikit-learn/ and installed with
su
I'm not really sure, but according to this that error happens when a package that depends on numpy is compiled targeting a specific version (or a specific platform), and that package is then installed in a different environment. How did you install those two packages? (numpy and scipy)
I'd suggest uninstalling both and then reinstalling SciPy, either using pip or from source.