I have to make a table that is quite long so I use the longtable package. The following code gives me the Something's wrong--perhaps a missing \item error for the \begin{center} line.
\documentclass[a4paper, 12pt]{article}
\usepackage[frenchb]{babel}
\usepackage[T1]{fontenc}
\usepackage{float}
\usepackage{caption}
\usepackage{xltabular}
\usepackage{longtable}
\usepackage{hyperref}
\begin{longtable}[H]{c|c|c|c|c|c}
\begin{center}
\hline
\textbf{ID projet} & \textbf{Nom du projet} & \textbf{Complexité} & \textbf{Disponibilité des données} & \textbf{Coût} & \textbf{Impact} \\
\hline
cell & cell & cell & cell & cell & cell \\
\hline
cell & cell & cell & cell & cell &cell \\
\hline
cell & cell & cell & cell & cell \\
\hline
cell & cell & cell & cell & cell & cell \\
\hline
cell & cell & cell& cell & cell & cell \\
\hline
cell & cell & cell & cell & cell & cell \\
\hline
cell & cell & cell & cell & cell & cell \\
\hline
\end{center}
\end{longtable}
I don't know if it's related but the first \hline gives me the Misplaced \noalign error and the \textbf line gives me the Misplaced \omit error.