I get the error mentioned in the title of the question. Can you help me please ?
\begin{table}[htb!]
\centering
\caption{\textit{others criterias : first scenario}} \label{Table2}
\resizebox{0.5\columnwidth}{!}{%
\begin{tabular}{c|ccc|cccc|c}
&\multicolumn{3}{c}{\underline{Instances}}
&\multicolumn{4}{c}{\underline{DPA}}
&&
&Staff &Activities &periods &EA &EB &TG-AV &RV-TD \\ \hline
&3 &72 &10 &477 &47 &178 &1421 \\
\hline
&3 &72 &10 &1087 &34 &207 &1170 \\
\hline
&3 &72 &10 &1415 &22 &215 &932 \\
\hline
&5 &120 &10 &1925 &1977 &485 &1897 \\
\hline
&5 &120 &10 &457 &552 &216 &1123 \\
\hline
&6 &140 &10 &1605 &1981 &347 &3039 \\
\hline
\end{tabular}%
}
\end{table}
&&
instead of\\
in the line before&Staff