# Overleaf: error in generating bibliography Undefined control sequence with \printbibliography

I am working fine on my Overleaf document until I inserted citation when the following error appears after using \printbibliography to generate reference list.:

Undefined control sequence.                      main.tex line 60
The compiler is having trouble understanding a command you have used. Check that the command is spelled correctly. If the command is part of a package, make sure you have included the package in your preamble using \usepackage{...}.
namepartfamily ->Zim\x
{fffd}\x {fffd}nyi
l.60 \end
{document}
The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., \hobx'), type I' and the correct
spelling (e.g., I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.


This error disappears when \printbibliography is commented out, but then no reference list generated. I can confirm I added all required packages. See the document below:

\documentclass[a4paper,10pt]{report}
\usepackage{biblatex}
\usepackage{graphicx}
\usepackage[top=25mm, bottom=25mm, left=25mm, right=25mm]{geometry}

\begin{document}

\input{titlepage}
%Table of content
\tableofcontents

%Abasract page
\newpage
\Large
\begin{center}
\textbf{\textit Abstract}
\end{center}
\hspace{10pt}

%\normalsize
This is a simple one-page abstract template. Please keep your abstract length at one page. The abstract should be in English.
\newpage

%begin main document
\chapter{Introduction}

\section{Statement of Problem}
This is the beginning of the introduction section.
%\subsection{Research Questions}
\section{Motivation}

\section{Research Objectives}

\section{Pre-Thesis Structure}

%===CHAPTER TWO ===
\chapter{Fundamental Concepts}

%=== CHAPTER THREE ===
\chapter{State of the Art}
\section{Transport}

%=== CHAPTER FOUR ===
\chapter{Material and Methods}

%=== CHAPTER FIVE ===
\chapter{Pilot Study}

%=== Reference Lists ====

\printbibliography
\end{document}

• Sounds like some character problem. Check in your .bib file and search for the text Zim, and check the character after it: you might need to re-type it carefully e.g. Zimányi or Zim\'{a}nyi (or similar—Zimányi was the top search result I got when googling Zim.?nyi on Google Scholar) – LianTze Lim Aug 19 at 1:28
• Yes, seems as though Zim?ny is malformed. If LianTzeLim's guess that it should be Zimányi is correct, the issue is probably that the á is not encoded as Biber/biblatex expects. The easy solution would be that your .bib file is UTF-8, but LaTeX expects US-ASCII. Did you try adding \usepackage[utf8]{inputenc} to your document? But maybe the á is malformed. Did you try deleting and re-writing the name? In any case you should clear the cache after you made the changes to avoid errors hanging about in temporary files: overleaf.com/learn/how-to/Clearing_the_cache – moewe Aug 19 at 5:01
• Ah, you're right. adding the package \usepackage[utf8]{inputenc} fix the problem. – arilwan Aug 19 at 10:22

Your .bib file probably contains a line like

author  = {József Zimányi},


(all credits for the detective work of figuring out the name go to LianTze Lim in the comments). Quite likely your .bib file is encoded in UTF-8 or another non-ASCII encoding.

But with your preamble (and the outdated TeX system on Overleaf) LaTeX expects US-ASCII input only (a more current LaTeX will use UTF-8 as default encoding). The easiest way to get things to work again is to tell LaTeX you want to use UTF-8 with

\usepackage[utf8]{inputenc}
`

You may have to clear the cache (see https://www.overleaf.com/learn/how-to/Clearing_the_cache) before you can recompile cleanly after that, but then you should get the desired output.