Probably I'm going to bother all of you, but I really don't understand where the problem is. Here follows a snapshot of my error:

It is a common error, but I'm quite sure my code is ok! The error is provided by this code:
\begin{table*}[hbt]%
\centering%
\tabcolsep2mm \small %
\begin{tabular}{c|c|c|c|c|c}
\multicolumn{3}{c}{y:5} & \multicolumn{3}{c}{x:10}
\end{tabular}
\caption{A caption.}%
\label{tab:des}%
\end{table*}%
However, If I don't use \multicolumn everything is compiled fine, e.g.:
\begin{table*}[hbt]%
\centering%
\tabcolsep2mm \small %
\begin{tabular}{c|c|c|c|c|c}
a & b & c & d & e & f
\end{tabular}
\caption{A caption.}%
\label{tab:des}%
\end{table*}%
What am I missing? Isn't \multicolumn available by default?
EDIT
Upon request, here follows the code. Please, notice that I'm using elsart.sty, the style file from Elsevier.
\documentclass[3p,twocolumn,number,referee,compress]{elsarticle}
\usepackage{graphicx}
\usepackage{caption}
\usepackage{subcaption}
\usepackage{amssymb}
\usepackage{amsthm}
\usepackage{color}
\raggedbottom
\usepackage{lineno}
\usepackage{natbib}
\usepackage[fleqn]{amsmath}
\usepackage{booktabs}
\usepackage[USenglish]{babel}
\journal{xxx}
\begin{document}
\begin{frontmatter}
\title{xxx}
\begin{abstract}\end{abstract}
\begin{keyword}\end{keyword}
\end{frontmatter}
\begin{table*}[hbt]%
\centering%
\tabcolsep2mm \small %
\begin{tabular}{c|c|c|c|c|c}
\multicolumn{3}{c}{y:5} & \multicolumn{3}{c}{x: 10}
\end{tabular}
\caption{.}%
\label{tab:des}%
\end{table*}%
\bibliographystyle{elsarticle-num}
\bibliography{References}
\end{document}
\endinput
With this code the error is:

\multicolumn, not\multicol. – Ian Thompson Jan 15 at 11:33å(if I read correctly); probably the text has some invisibile characters: fix it and retry. – egreg Jan 15 at 13:13