Hello.

> john at molehole:~ > latex Symbol_class.tex
> This is TeX, Version 3.14159 (Web2C 7.3.1)
> (Symbol_class.tex
> LaTeX2e <1999/12/01> patch level 1
> Babel <v3.6Z> and hyphenation patterns for american, french, german,
> ngerman, n
> ohyphenation, loaded.
> ! Undefined control sequence.
> l.4 {\sf

Ah, this is a macro for the default Sans Serif font under TeX... I guess
it's not defined in LaTeX.  If you check out the TeXFileOut package,
you'll see that it can be configured to use other macros for Sans Serif
fonts.  Take a look at TeXFileOut>>setDefaultFonts.  Alternatively, you
may replace all occurrences of \sf with something else that selects a
Sans Serif font in LaTeX.

Hope this helps,
Andres.