`Missing } inserted' when apacite is loaded; no error when it's not loaded

Question

I'm writing a thesis, and want to use the APA citation style. I've installed the apacite package. Possibly incorrectly, but TeXworks does not give any errors concerning the package. It does give errors with all \cite{} commands, which seem to mess up with the \begin{} and \end{} commands. If I comment out the \usepackage{apacite} statement, everything works just fine (even if I keep the bibliographystyle apacite!) Anyone who has any idea what could be happening here? Thanks in advance!

Some example errors:

! Missing } inserted.

l. 19 Charles Darwin on language \cite{Darwin71}

?

! Too many }'s.

l.20

?

!Latex error: \begin{document} ended by \end{quote}

And this is the master file I try to typeset:

\documentclass[10pt]{book} 

\usepackage{url}
\usepackage{geometry}
\usepackage{comment}
\usepackage{pdflscape}
\usepackage{natbib}
\usepackage{titling}
\usepackage{amsmath} 
\usepackage{amssymb} 
\usepackage{appendix}
\usepackage{makeidx} %If you want to generate an index, automatically 
\usepackage{graphicx}
\usepackage{tipa}
\usepackage{apacite}

\begin{document} 

\author{Ellen Maassen} 
\title{Language as a Threefold Adaptive System \newline\\ {\Large The Emergence of Phonological Compositionality}}
\date{\today} 

\maketitle

\frontmatter
\tableofcontents 
\include{preface}

\mainmatter 
\input{chaptr12}
\input{chaptr22} 
\input{chaptr32} 
\input{chaptr42} 
\input{chaptr52}  
\input{chaptr62}
\input{chaptr72}

\appendix
\input{Geluidjes}
\input{bootstrapping}

\backmatter  
\bibliographystyle{apacite} 
\bibliography{refs} 
\printindex 

\end{document}

Answer 1

This problem can be resolved simply loading the package natbib after apacite.

Note that you can avoid loading natbib if you pass the option natbibapa to apacite.

\usepackage[natbibapa]{apacite}

In this way apacite loads natbib with the options longnamesfirst and sort, needed in order to meet the APA specifications.