One of the more common mistakes in running LaTeX is to read in old versions of packages instead of the new versions. If you get an incomprehensible error message from a standard package, make sure you are loading the most recent version of the package. You can find out which version of the package has been loaded by looking in the log file for a line like:
Package: fred 1994/06/01 v0.01 Fred's package.You can use the <release-date> options to
\usepackageto make sure that you are getting a suitably recent copy of the document class or package. This is useful when sending a document to another site, which may have out-of-date software.