[Tex/LaTex] More than 26 appendices

appendicesnumbering

For my thesis I have a document that contains more than 26 appendices. The appendices 1 up to 26 are are alphabetical numbered as A up to Z. However at the 27th appendix I get an error (although I though that LaTeX would automatically number the 27th appendix as AA):

! Undefined control sequence.
\GenericError ...
#4 \errhelp \@err@ ...
l.1133 ...{Elaborated interview team leader}
\label{appendixaa}
?

At line 1133 starts the 27th appendix. I was looking for the content of a generic error but are not getting anything wiser. I use sections in my appendix, because my documentclass is article which is more controlable in layout in my opinion:

\section{Elaborated interview team leader}\label{appendixaa}

Any idea how to solve this issue?

UPDATE 24/09/2013

I have done what Erreg suggested, but now the message is that appendix.tex could not be found:

My mainfile (thesis.tex):

 \documentclass[11pt,a4paper]{article}

    \usepackage{appendix}
    \usepackage{alphalph}

\renewcommand\thesection{\AlphAlph{\value{section}}}

    \include{Sections/appendix}

    \end{document}

In the map Sections, appendix.tex is the file with all appendices:

\appendix
\input{appendix}

\section{ appendix a}\label{appendixa}
\pb

\section{appendix b}\label{appendixb}
\pb

\setcounter{section}{25}

\section{appendix z}\label{appendixz}
\pb

\section{appendix aa}\label{apendixaa}
\pb

\section{appendix ab}\label{apendixab}
\pb

\section{appendix ac}\label{apendixac}
\pb

UPDATE:03/10/2013
This is what i have now:
thesis.text (main file):

\documentclass[11pt,a4paper]{article}

%Enabled packages
\usepackage{appendix}

\begin{document}

\tableofcontents


\include{Sections/appendix}

\end{document}

appendix.text (in the subfolder Sections):

\appendix

\setcounter{section}{24} % just to see the effect

\section{Twenty five}

\section{Twenty six}

\section{Twenty seven}

The error I get now is: 

! LaTeX Error: Counter too large.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              

l.33 \section{Twenty seven}

Above example is the same as Ergg provided. Any idea? I do not see the light anymore.

Best Answer

There is a package also for this, called alphalph.

\documentclass{book}

\usepackage{alphalph,etoolbox}
\appto\appendix{% patch \appendix so \AlphAlph is used
  \renewcommand\thechapter{\AlphAlph{\value{chapter}}}%
}

\begin{document}

\appendix
\setcounter{chapter}{24} % just to see the effect

\chapter{Twenty five}

\chapter{Twenty six}

\chapter{Twenty seven}

\end{document}

Rather than the output, I'll show the relevant part of the terminal output:

Appendix Y.
[1][2]
Appendix Z.
[3] [4]
Appendix AA.

This assumes that the documentclass has chapters; if your document class is article or a similar one which has sections at the top level, use 

\renewcommand\thesection{\AlphAlph{\value{section}}}

as the text of the patch.

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