[Tex/LaTex] Missing \endcsname inserted. \protect

missing

I am getting the following error code:

./main.aux:113:
Missing \endcsname inserted.
<to be read again> 
                   \protect 
l.113 ... find region o

f proportionality}{{1}{10}}

Minimum working example (long due to vague error):

\documentclass[a4paper]{article}
\usepackage[utf8x]{inputenc}
\usepackage{amsmath}
\usepackage{graphicx}
\usepackage{graphics}
\usepackage[utf8x]{inputenc}
\usepackage{siunitx}
\usepackage{filecontents}
\usepackage{amsmath}
\usepackage[titletoc]{appendix}
\usepackage{mathtools}
\usepackage{subcaption}
\usepackage{caption}
\usepackage[verbose]{placeins}
\graphicspath{ {images/} }

\begin{document}

%the following section is included as it is around line 113
text $^{241}\textrm{Am}$ text 
\begin{equation}
^{241}_{95}\textrm{Am}\rightarrow ^{237}_{93}\textrm{Np}+^4_2\alpha
\end{equation}

%the following section is included as it is the last bit i worked on
\section{text}

text B$\textrm{F}_3$ text

\begin{figure}[h]
\includegraphics[scale=0.5]{file.png}
\centering
\caption{text B$\textrm{F}_3$ text}
\label{text}
\end{text}

\section{text}

\section{text}

\bibliographystyle{ieeetr}
\bibliography{references}

\section{Appendices}
\subsection{Appendix A}

\begin{table}[h]
\centering
\caption{text B$\textrm{F}_3$ text}
\label{text}
\begin{tabular}{|c|c|}
\hline
data taken from table generator so v.likely correct
\end{tabular}
\end{table}


\end{document}

Best Answer

./main.aux:113:
Missing \endcsname inserted.
<to be read again> 
                   \protect 
l.113 ... find region of proportionality}{{1}{10}}

The error is caused by line 113 in the *.aux file, not the .tex file. The end of line 113 looks like a label definition with an entity (section, equation, figure, ...) numbered with 1 on page 10.

The label name in \label{...} must survive a \csname ...\endcsname. Thus, my suspicion is that the label name contains stuff (non-ASCII letters, ...) that breaks in the .aux file.

Related Question