# Underfull \hbox (badness 10000) detected at line XX []$[]$

I know there were a lot of questions regarding underfull hbox, but in my case error

Underfull \hbox (badness 10000) detected at line 5
[]$[]$


point to line

5: \begin{document}


How can hbox be underfull if compilation of the document has not even started?

EDIT: after inspection I have found out that autonum package is creating this error.

\documentclass{article}

\usepackage{autonum}

\begin{document}
\end{document}

-

It is a bug in package autonum, as @Heiko Oberdiek mentioned in his answer in question autonum-does-not-work-with-eqnarray.

Please report the bug to the maintainer of autonum.

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I've reported the bugs to the email provided with the autonum package. –  Pygmalion Aug 22 '12 at 16:52
Thanks for mentioning. I just uploaded version 0.3.1 which should fix this bug. –  Patrick Häcker Aug 25 '12 at 16:10