So, I am writing my first big document - but I try to remain simple. And I have some problems. I am trying to solve one at a time.
First the title page.
\documentclass[10pt,a4paper]{book}
\usepackage[a4paper]{geometry}
\usepackage[utf8]{inputenc}
\usepackage[francais]{babel}
\usepackage[T1]{fontenc}
\usepackage{titling}
%\usepackage{showframe}
\usepackage{graphicx}
\usepackage{listings, multicol, color, fancyhdr,lastpage}
\usepackage[font=small,format=plain,labelfont=bf,up,textfont=it,up]{caption}
\usepackage[hyperindex=true,colorlinks=true,breaklinks=true,linkcolor=blue]{hyperref}
\title{\huge\bsc{Des chiffres et des lettres}}
\author{Stéphane \bsc{22Decembre Guedon}}
\date{13 mai 2015}
% fonte
\renewcommand{\familydefault}{\sfdefault}
\posttitle{
\newline
%\vspace{1cm}
\Large\emph{Protéger ses communications en ligne\\et autres aspects de sa vie numérique}\\
\vspace{5mm}
\LARGE\emph{GnuPG et OpenPGP pour tous}\\
}
\preauthor{
\vspace{5mm}
\includegraphics[width=0.9\textwidth]{./images/logo-gnupg}\\
\vspace{1cm}\\
}
\predate{version 1 du }
\begin{document}
\maketitle
%\frontmatter
%\include{preambule-court}
\tableofcontents
\include{0-intro}
\include{1-alternatives}
…
\end{document}
I get the following errors:
Extra }, or forgotten \endgroup.
There's no line here to end.
Misplaced \crcr.
Extra }, or forgotten $.
\begin{center} on input line 55 ended by \end{tabular}.
All the errors refer precisely to the blank line just after \maketitle