If you get the following error:

    LaTeX error.  See LaTeX manual for explanation.
		  Type  H <return>  for immediate help.
    ! Can be used only in preamble.
    \@latexerr ...for immediate help.}\errmessage {#1}

    l.23 \documentstyle
		       [vi,12pt,tgrind]{mitthesis}


the most probably cause for this error is that you are using a very
old (and latex2.09) version of the mitthesis class.  You can get the
right version by typing:

	attach thesis
	cp /mit/thesis/tex/mitthesis.cls .

Then, you'll probably want to change your main.tex from
      \documentstyle{mitthesis}
to
      \documentclass{mitthesis}	

Then try latexing again.