package titling, but still problem with \preauthor

Question

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

Answer 1

The reason is that titling wants pairs \presomething{} … \postsomething{}: if one of them is here, the other must be too. I don't know if it's a bug or a feature. I managed to find a logo (not a vector logo, despite its .pdf extension), so I could compile:

\documentclass[10pt,a4paper]{book}
\usepackage[a4paper]{geometry}

\usepackage[utf8]{inputenc}
\usepackage[francais]{babel}
\usepackage[T1]{fontenc}
\usepackage{lmodern}

\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}
\pretitle{}

\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}\\
    }

\postauthor{}
\predate{version 1 du }
\postdate{}

\begin{document}

\maketitle

\end{document}