Re: \LaTeX command produces error

I've made some progress with this code:
\catcode`\@ = 11

But I am now finding errors with this statement:

\def\withlinenumbers{\relax
\def\@oddfoot{\hbox to 0pt{\hss\LineNumberRuler\hskip
1.5pc}\hfil}\relax
\def\@evenfoot{\hfil\hbox to 0pt{\hskip
1.5pc\LineNumberRuler\hss}}}

If I comment it out the file compiles. Is there a problem with the
syntax in that definition? The error output by the compiler is:

sysdsgn.doc.tex:72: Undefined control sequence.
\@thefoot ->\hbox to 0pt{\hss \LineNumberRuler
\hskip 1.5pc}\hfil

Thanks

.