How to fix error Missing number, treated as zero

I know this must be a common title for a question, and I have done my research but I still can't figure out why i get this error with this block of code:

\documentclass{sig-alternate}
\usepackage[british]{babel}
\usepackage{fancyhdr}
\usepackage{booktabs}
\usepackage[utf8]{inputenc}
\usepackage{libertine}
\usepackage{balance}
\usepackage{hyperref}
\usepackage{url}
\graphicspath{ {./images/} }

\setlength{\heavyrulewidth}{1.2pt}
\setlength{\lightrulewidth}{0.7pt}
\pagestyle{fancy}
\rhead{UMAP’17, July 9-12, 2017, Bratislava, Slovakia}

\renewcommand{\footrulewidth}{}
\newfont{\mycrnotice}{ptmr8t at 7pt}
\newfont{\myconfname}{ptmri8t at 7pt}
\let\crnotice\mycrnotice
\let\confname\myconfname

\begin{document}
\title{Improving Cold Start Recommendation by Mapping
Feature-Based Preferences to Item Comparisons}

\numberofauthors{2}

\author{
\alignauthor
Saikishore Kalloori\\
\affaddr{Free University of Bozen - Bolzano,}\\
\affaddr{Piazza Domenicani 3, I - 39100,}\\
\email{ksaikishore@unibz.it}
\alignauthor
Francesco Ricci\\
\affaddr{Free University of Bozen - Bolzano,}\\
\affaddr{Piazza Domenicani 3, I - 39100,}\\
\email{fricci@unibz.it}
}
\maketitle
\section{EXPERIMENTAL EVALUATION}\noindent
\subsection{Data Set}\noindent
In order to test our hypothesis we needed a dataset containing both
item and feature preferences. The only publicly available data set
with such preferences, which we could identify, is the PoliMovie
dataset \cite{10}. For each user in the dataset, there are preferences
expressed explicitly for movies and for their features, in the form
of likes.
\bibliographystyle{abbrv}
\bibliography{zdroje}
\end{document}


Error is pointed to the first line with \section. It says:

Missing number, treated as zero. Overfull \hbox(1.82866 pt too wide) in paragraph at lines 140--154.

I have couple of errors like this scattered throughout the whole document near \section commands. I see only couple of lines highlighted with this error(no other kinds of errors appear) but overleaf says that I have 37 errors, even though the document compiles OK, and looks just like it's supposed to look. Any ideas how to fix this error? Thank you for your help and time.

• (1) welcome, (2) please post a full minimal example instead of just a sniplet. This can be caused by all sorts of things, but without a proper context example the others can just copy and test as is, it is very difficult to help you. – daleif Oct 18 '18 at 10:43
• It's quite unlikely that the code above issues a “Missing number” error, unless you have redefined \section (possibly via packages). Thus a minimal example is needed. By the way, \noindent is redundant and you should remove it. – egreg Oct 18 '18 at 10:51
• You should never trust the output if you got errors, even if it looks sort of OK. Unfortunately, the error you got is very generic and can be caused by many different things. The code shown in the question looks OK-ish w.r.t. the error (I'd not write \section{RELATED WORK}, instead I'd tell the class to format sections in ALL CAPS, of that is desired; I would also not use \noindent, if it is necessary at all - which is not clear - it could instead be done automatically; I would not use numeric-labels as bibkeys, I would use recognisable names such as sigfridsson or liggett:ips). ... – moewe Oct 18 '18 at 10:52
• OK, if you say so. Where can we find sig-alternate? We also don't have zdroje.bib, so we can't run your exact code, but we may be able to see the error without that file. – moewe Oct 18 '18 at 11:47
• \renewcommand\headrulewidth{0pt} is the correct command – egreg Oct 18 '18 at 12:19

The answer was posted by user @egreg, I just needed to change commands:

\renewcommand\headrulewidth{}
\renewcommand{\footrulewidth}{}


to:

\renewcommand\headrulewidth{0pt}
\renewcommand{\footrulewidth}{0pt}


The issue was connected with package fancyhdr,as user @moewe pointed out. Thank you all for your help.