# Compilation Error "! Missing \endcsname inserted" The control sequence marked <to be read again> should not appear between \csname and \endcsname

   ! Missing \endcsname inserted.
\begingroup
l.52 ...}intopreamble]Deobfuscation}{{4.1.1}{xii}}
The control sequence marked <to be read again> should
not appear between \csname and \endcsname.
(D:\DH\Luan_Van_Tot_Nghiep\Latex\triet_thesis_test\LVTN.aux

• Please show use some code (Minimal working example). Nov 26 '13 at 16:09
• On overleaf, I just deleted the cache and aux and other files. It solved the problem. Sep 22 '18 at 17:39

You have a wrong character in one of your labels:

\subsection{LLVM}
\label{subsec:LLVMDeobfuscation}


where, between LLVM and Deobfuscation, you have the Unicode character U+200E (LEFT-TO-RIGHT MARK) that somehow sneaked in.

Retype the label and you should be OK.

• Thank you. I really appreciate your help. Could you tell me how you find out the reason :) ? Nov 26 '13 at 17:37
• If you use the \usepackage{underscore} the '_' character in labels will cause this error. To fix this also use \usepackage[english]{babel} Dec 7 '15 at 12:07
• I'm stuck with this error message, and I would love to know how I go about fixing it? Mar 28 '18 at 15:14
• @AndreasStorvikStrauman Difficult to say without an example. Mar 28 '18 at 15:50
• @AndreasStorvikStrauman I copied the offending text and pasted on a multiconverter that shows every byte, for instance r12a.github.io/app-conversion Mar 28 '18 at 17:21

For others if you have not tried to delete all the generated files from pdflatex and bibtex, then do that before any other changes, because it could be a compilation error.

I never wrote Vietnamese and don't know if it can be done with pdflatex. However, if I use xelatex instead and

\documentclass[a4paper,oneside]{report}
%\usepackage[utf8x]{vietnam}%% xelatex is by default utf8
\usepackage{graphicx}
\usepackage{pdfpages}
\usepackage{suthesis-2e}
\begin{document}
...


I'll get a proper output with out any errors.

• Unfortunately, I have to write my thesis in Vietnamese :( . Could you help me a little bit further? Nov 26 '13 at 16:36
• as I wrote: use may preamble and then run xelatex instead of pdflatex. Every editor ahopuld have such a button or topix for xelatex
– user2478
Nov 26 '13 at 16:41
• No, the OP probably won't get proper output: the error is caused by a spurious (invisibile) character in a label and probably all references to it will not be resolved. Nov 26 '13 at 17:45
• I get all references right with xelatex
– user2478
Nov 26 '13 at 18:29
• You get references right provided you build \ref{...} by copy-pasting from the argument of \label. If you type directly \ref{subsec:LLVMDeobfuscation} you can't get a correct reference. Nov 27 '13 at 11:17

If you use \usepackage{underscore} the '_' character in labels will cause this error.

To fix this add the following: \usepackage[english]{babel}