# Having problems with \longtable and \multicolumn

I'm trying to put a header in a table generated with a \longtable environment, but \multicolumn gives @multispan error. Here is my piece of code:

\documentclass[a4paper,11pt]{article}
\usepackage{graphicx}
\usepackage{longtable}
\usepackage{booktabs}
\usepackage{colortbl}
\usepackage[table]{xcolor}
\usepackage{siunitx}
\usepackage{tabu}
\usepackage{enumerate}
\usepackage{tabularx}

\begin{document}

\begin{longtabu} to \linewidth { | X[6,l] | X[1,c] | }
\toprule
\rowcolor{gray!20}
\multicolumn{2}{|l|}
{\sc 4 -- program} &
\\\midrule
\hiderowcolors
%%%%%%%%%%%%%%%%%%%%%%
A &
06
\\\midrule
%%%%%%%%%%%%%%%%%%%%%%
\bottomrule
\end{longtabu}

\end{document}


I need it to be a long table at the first moment because I am sure that the table is longer than one page. I've already tried others packages (tabularx, longtable, etc) with no success.

Maybe someone would help me to find the error?

latexpdflatexlongtable