Error in tcolorbox Missing \endcsname inserted

I am trying to a fancy theorem type for my notes. I like tcolorbox examples. But the one that I like most is giving me an error.

    Missing \endcsname inserted.


This one is on page 360 of the tcolorbox manual. I do not understand why I am getting this error and how to fix. There was a similar question

https://tex.stackexchange.com/questions/174017/compile-error-missing-endcsname-inserted-with-code-and-tcolorbox


But it did not solve my problem. The result should be like this

    \documentclass[11pt]{article}
\usepackage{varioref}
\usepackage{cleveref}
\tcbuselibrary{skins}

\newtcbtheorem[use counter from=Definition]{YetAnotherTheorem}{Theorem}%
{theorem style=change apart,enhanced,arc=0mm,outer arc=0mm,
boxrule=0mm,toprule=1mm,bottomrule=1mm,left=1mm,right=1mm,
titlerule=0mm,toptitle=0mm,bottomtitle=1mm,top=0mm,
colframe=red!50!black,colback=red!5!white,coltitle=red!50!black,
title style={top color=yellow!50!white,bottom color=red!5!white,
middle color=yellow!50!white},
fonttitle=\bfseries\sffamily\normalsize,fontupper=\normalsize\itshape,
}{theo}

\begin{document}
\begin{YetAnotherTheorem}{Mittelwertsatz f\"{u}r $n$ Variable}{mittelwertsatz_n2}% Es sei $n\in\mathbb{N}$, $D\subseteq\mathbb{R}^n$ eine offene Menge und
$f\in C^{1}(D,\mathbb{R})$. Dann gibt es auf jeder Strecke
$[x_0,x]\subset D$ einen Punkt $\xi\in[x_0,x]$, so dass gilt
\begin{equation*}
\end{equation*}
\end{YetAnotherTheorem}

\end{document}

• One obvious point: you're not even loading tcolorbox. – user121799 Nov 27 '18 at 2:52
• @marmot I am actually loading tcolorbox package I just forgot to put it here – Kumarm Nov 27 '18 at 3:03

This is too long for a comment. You have several issues:

• you need to add \tcbuselibrary{theorems}
• you have not defined \mathbb
• the use counter from=Definition does not work because you have not defined a definition environment. As per the comments, I have replaced this with no counter to remove the numbering.

The following code compiles and perhaps does what you want:

\documentclass[11pt]{article}
\usepackage{amssymb}
\usepackage{varioref}
\usepackage{tcolorbox}
\tcbuselibrary{skins,theorems}
\usepackage{cleveref}

\newtcbtheorem[no number]{YetAnotherTheorem}{Theorem}%
{theorem style=change apart,enhanced,arc=0mm,outer arc=0mm,
boxrule=0mm,toprule=1mm,bottomrule=1mm,left=1mm,right=1mm,
titlerule=0mm,toptitle=0mm,bottomtitle=1mm,top=0mm,
colframe=red!50!black,colback=red!5!white,coltitle=red!50!black,
title style={top color=yellow!50!white,bottom color=red!5!white,
middle color=yellow!50!white},
fonttitle=\bfseries\sffamily\normalsize,fontupper=\normalsize\itshape,
}{theo}

\begin{document}

\begin{YetAnotherTheorem}{Mittelwertsatz f\"{u}r $n$ Variable}{mittelwertsatz_n2}% Es sei $n\in\mathbb{N}$, $D\subseteq\mathbb{R}^n$ eine offene Menge und
$f\in C^{1}(D,\mathbb{R})$. Dann gibt es auf jeder Strecke
$[x_0,x]\subset D$ einen Punkt $\xi\in[x_0,x]$, so dass gilt
\begin{equation*}
\end{equation*}
\end{YetAnotherTheorem}

\end{document}


The output is:

Edit To remove both the theorem name and number and just have the box itself, it is better to use newtcolorbox, to give:

Here is the updated code:

\documentclass[11pt]{article}
\usepackage{amsmath,amssymb}
\usepackage{varioref}
\usepackage{tcolorbox}
\tcbuselibrary{skins}
\usepackage{cleveref}

\newtcolorbox{YetAnotherTheorem}[1]%
{enhanced,arc=0mm,outer arc=0mm,
boxrule=0mm,toprule=1mm,bottomrule=1mm,left=1mm,right=1mm,
titlerule=0mm,toptitle=0mm,bottomtitle=0mm,top=0mm,
colframe=red!50!black,colback=red!5!white,coltitle=red!50!black,
colbacktitle=yellow!50!white,colback=red!5!white,
title=#1,
fonttitle=\bfseries\sffamily\normalsize,fontupper=\normalsize\itshape,
}

\begin{document}

\begin{YetAnotherTheorem}{Mittelwertsatz f\"{u}r $\mathbf{n}$ Variable}
$f\in C^{1}(D,\mathbb{R})$. Dann gibt es auf jeder Strecke
$[x_0,x]\subset D$ einen Punkt $\xi\in[x_0,x]$, so dass gilt
\begin{equation*}

• In my full document I have tcolorbox loded, I just forgot to put here. I have theorems loaded as well. It did not work. When I copy this and create a new document this works. – Kumarm Nov 27 '18 at 3:08
• @Kumarm From your comment it is not clear to me, has this solved your issue? For me I think that the \endcsname error was caused by the use counter from=Definition. Perhaps this was your problem? In any case, this was all that I changed in the \newtcbtheorem definition. – user30471 Nov 27 '18 at 3:18
• Yes you are right after replacing use counter from=Definition with number within=section this works. However actually I do not want the numbers at all when I delete use counter from=Definition part it still gives me 1. Can you help me how to get rid of the numbering at all. – Kumarm Nov 27 '18 at 3:23
• @Kumarm To remove the numbering, replace number within=section with no counter. I'll edit my post. – user30471 Nov 27 '18 at 3:27
• I know that this was the issue because I was just about to post a very similar answer in which just added \newtcbtheorem{Definition}{Theorem}% {colback=white,colframe=red!50!black,fonttitle=\bfseries, separator sign={\ $\blacktriangleright$}}{theo} to solve the issue, this also works. BTW, I'd use \boldmath for the theorem title to make $n$ bold as well. – user121799 Nov 27 '18 at 3:28