compiler complains about apacite

Question

I use the following packages in my document:

\documentclass[a4paper,12pt,twoside,BCOR=10mm]{scrbook}
% Packages
\usepackage{ucs}
\usepackage[utf8x]{inputenc}
\usepackage[icelandic, english]{babel}
\usepackage{t1enc}
\usepackage{graphicx}
\usepackage[intoc]{nomencl}
\usepackage{enumerate,color}
\usepackage{url}
\usepackage[pdfborder={0 0 0}]{hyperref}
\usepackage{appendix}
\usepackage{eso-pic}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage[nottoc]{tocbibind}
\usepackage[sort&compress,authoryear]{natbib}
\usepackage[sf,normalsize]{subfigure}
\usepackage[format=plain,labelformat=simple,labelsep=colon]{caption}
\usepackage{placeins}
\usepackage{tabularx}
% Configurations
\graphicspath{{figs/}}

When I add

\usepackage{apacite}

I get a bunch of errors, starting with:

! Undefined control sequence.
l.1203 \st@rtbibchapter

Note that apacite should be correctly included in my system as I use it without problems on another document.

Do you have any idea where is the problem?

Answer 1

From the apacite package documentation:

When you want to use natbib for citation and apacite for the reference list, you still need to load the LaTeX package apacite.sty (with \usepackage), because of the commands that are included in the BibTeX output. The best interoperability is obtained by loading apacite with the natbibapa option. There is then no need to load natbib explicitly, because apacite already does this.

So you should replace

\usepackage[sort&compress,authoryear]{natbib}
\usepackage{apacite}

with

\usepackage[natbibapa]{apacite}

From the t1enc package page on CTAN:

Ob­so­lete pack­age for ac­ti­vat­ing T1 font en­cod­ing. The re­place­ment fontenc pack­age with (op­tional) ar­gu­ment T1 does this task more sat­is­fac­to­rily.

So you should replace

\usepackage{t1enc}

with

\usepackage[T1]{fontenc}

Other notes on your omnibus preamble:

1. I don't use utf8 encoding in my source files often enough to provide a definitive answer on this point, but you may want to consider utf8x vs. utf8 (inputenc) for a discussion of the relative merits of utf8x/ucs and inputenc.
2. subfigure is deprecated; use subfig or subcaption instead.
3. koma-script (of which your class, scrbook, is a part) implements nearly all functionality from the caption package, so you should consider using the built-in class options instead of using caption.
4. hyperref should be loaded last, with only a few exceptions.

Here's the complete code:

\documentclass[a4paper,12pt,twoside,BCOR=10mm]{scrbook}
% Packages
\usepackage{ucs}
\usepackage[utf8x]{inputenc}
\usepackage[icelandic, english]{babel}
\usepackage[T1]{fontenc}
\usepackage{graphicx}
\usepackage[intoc]{nomencl}
\usepackage{enumerate,color}
\usepackage{url}
\usepackage{appendix}
\usepackage{eso-pic}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage[nottoc]{tocbibind}
%\usepackage[sort&compress,authoryear]{natbib}
\usepackage[natbibapa]{apacite} % use `natbibapa' option instead of `natbib` package
%\usepackage[sf,normalsize]{subfigure} % deprecated; use other means
%\usepackage[format=plain,labelformat=simple,labelsep=colon]{caption} % use class commands instead
\usepackage{placeins}
\usepackage{tabularx}

\usepackage[pdfborder={0 0 0}]{hyperref} % moved to end of packages

\begin{document}
Test
\end{document}