Some (rather modern) packages are written using the LaTeX3 programming environment. Since LaTeX3 is still under development, the author cannot reliably guess what version of LaTeX3 the user has installed, and whether that version is adequate for the current package. Thus the package’s code often checks the user’s installation, and complains if it’s older than the author’s installation at time of testing. The error message is:
The “additional help” tells you the solution: update your LaTeX3 installation. The relevant things are l3kernel (the programming environment, which contains the expl3 mentioned in the error message) and l3packages (LaTeX3 constructs such as command definitions).! Support package expl3 too old.
While this sounds a drastic remedy, it is no longer the major
undertaking it once was — if you are using a modern TeX
distribution that you installed yourself, ask it to update over the
internet; if that choice is not available, install from the
tds.zip files available for both packages on CTAN.
This answer last edited: 2013-02-20
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=expl3-old