tcb/shadow is not known

Question

I've installed the latest version of pgf and tcolorbox but I still get an error :

I do not know the key 'tcb/shadow'...

The following is the first part of the preamble

\documentclass[xcolor=svgnames,a5paper]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}

\usepackage[frenchb]{babel}
\usepackage{multicol}
\usepackage{amssymb,amsmath,amsthm,amsfonts}
\usepackage{cases}
\usepackage[svgnames]{xcolor}
\usepackage{tcolorbox}
\tcbuselibrary{skins}
%\usepackage{tikz}
\usepackage{tkz-tab}
\usepackage{tkz-base}
%\usepackage{tkz-arith}
\usepackage{tkz-fct}
\usepackage{tkz-tukey}
\usepackage{pgfplots}
\pgfplotsset{width=10cm,compat=newest}


\usetikzlibrary{arrows,decorations.pathmorphing,shadows}
\usepackage{mdframed, graphicx, xkeyval,ifthen, ifpdf, etoolbox}
\usepackage{tabularx}

\usepackage{pifont}

\usepackage{colortbl}
\usepackage[tikz]{bclogo}

\usepackage{alterqcm}


\usepackage{mdframed, graphicx, xkeyval,ifthen, ifpdf, etoolbox,fp,calc}

\usepackage{fancybox}

\usepackage{framed}
\usepackage[right]{eurosym}
\usepackage{multicol}
\providecommand{\subtitle}[1]{%essai commande de sous-titre
  \usepackage{titling}
  \posttitle{%
    \par\large#1\end{center}}
}

\frenchbsetup{StandardLists=true}
\usepackage{enumitem}
\setlist[itemize,1]{label=$\diamond$}
\setlist[itemize,2]{label=$\bullet$}
\usepackage{fancyhdr}
\pagestyle{fancy}

\usepackage{answers}
\usepackage{lmodern}
\usepackage{textcomp} % provides euro and other symbols


\usepackage{hyperref}
\hypersetup{
            colorlinks=true,
            linkcolor=blue,
            citecolor=Blue,
            urlcolor=Blue,
            breaklinks=true}
\urlstyle{same}  % don't use monospace font for urls

\usepackage[margin=2cm]{geometry}

And here is the code for a \newcommand which uses tcolorbox

\newcommand{\imps}[2]{%
\tcbset{skin=enhanced,colback=red!5!white,
  colframe=red!75!black,fonttitle=\bfseries}

\begin{tcolorbox}[skin=beamer,shadow={2mm}{-1mm}{0mm}{gris0!80!white},width=#1cm]
#2.
\end{tcolorbox}
}

Thanks a lot for your help

TeXwriter 1.6.9 : Android

An error occures using the option "most" or "all" Here is a shorter document to help you.

\documentclass[xcolor=svgnames,a5paper,]{article}
\usepackage[utf8]{inputenc}
\usepackage{pgfplots}
\pgfplotsset{width=10cm,compat=newest}

\usepackage{colortbl}

\usepackage{tcolorbox}
\tcbuselibrary{skins}

\definecolor{gris}{gray}{.80}
\newcommand{\imps}[2]{%
\tcbset{skin=enhanced,colback=red!5!white,
  colframe=red!75!black,fonttitle=\bfseries}

\begin{tcolorbox}[skin=beamer,shadow={2mm}{-1mm}{0mm}{gris!80!white},width=#1cm]
#2.
\end{tcolorbox}
}
\begin{document}
\imps{4}{L'abscisse figure toujours en première position et l'ordonnée en seconde position}
\end{document}

Answer 1

Here's an extract from the CHANGELOG file in the sources for tcolorbox:

version 2.31 (2013/06/18)
- several internal changes
[...]
- new shadow features for the 'skins' library with the options:
  'shadow', 'fuzzy shadow', 'drop shadow', 'drop fuzzy shadow', 'halo', 'fuzzy halo'

Indeed, if I compile your example with TeX Live 2013, I get no error; the error appears when I compile with TeX Live 2012.

Thus it appears that the TeX distribution shipped with your version of TeX Writer is quite old. I don't think you can upgrade just the TeX distribution without a (paid) yearly subscription to TeX Writer; however, in the developer’s site there’s no indication of what is the currently shipped version of TeX Live, so it’s best to ask the developer before paying.