I have a book written in LaTeX (WinEdt 9, Windows 7) that I cannot compile after I switched to a new computer (worked perfectly before). The error is You can't use prefix with "\begingroup on one of the \Newassociation-lines (package answers) in the minimal example below. The problems seems to be an incompatibility between packages, but I have not been able to pinpoint which package(s) that is the problem. In the example below the error is on the line \Newassociation{hint}{Hint}{hint}, but if I remove the \newtheorem-line, the error instead comes on the line \Newassociation{sol}{Solution}{sol}. I cannot get rid of the error by switching the order of the \usepackage commands as was recommended in another discussion here. Any suggestions?
\documentclass{book}
\usepackage{siunitx}
\usepackage{answers}
\usepackage{amsthm}
\usepackage{graphicx,epstopdf}
\usepackage[format=plain,font=small,labelfont=bf,up]{caption}
\usepackage[version=3]{mhchem}
\usepackage{float}
\usepackage{placeins}
\usepackage{pdfpages}
\usepackage{makeidx}
\usepackage{enumerate}
\usepackage{fixltx2e}
\usepackage{xspace}
\usepackage{textgreek}
\newtheorem{Ex}{Exercise}
\Newassociation{ans}{Answer}{ans}
\Newassociation{hint}{Hint}{hint}
\Newassociation{sol}{Solution}{sol}
\Newassociation{solt}{SolutionTeacher}{solt}
\begin{document}
Short text
\end{document}
—-more info—-
I believe that I am using at least quite recent versions of everything as my computer is less than a year old. I am running: This is pdfTeX, Version 3.1415926-2.5-1.40.14 (MiKTeX 2.9 64-bit) (preloaded format=pdflatex 2015.5.19)
I added \listfiles and used the suggested workaround (otherwise \listfiles would not work; the workaround also worked for the whole book document) and got the following:
*File List*
book.cls 2007/10/19 v1.4h Standard LaTeX document class
bk10.clo 2007/10/19 v1.4h Standard LaTeX file (size option)
siunitx.sty 2015/01/21 v2.6e A comprehensive (SI) units package
expl3.sty 2015/03/01 v5547 L3 programming layer (loader)
expl3-code.tex 2015/03/01 v5547 L3 programming layer
etex.sty 1998/03/26 v2.0 eTeX basic definition package (PEB)
l3unicode-data.def 2015/03/01 v5544 L3 Unicode data
l3pdfmode.def 2015/03/01 v5544 L3 Experimental driver: PDF mode
xparse.sty 2014/11/25 v5471 L3 Experimental document command parser
amstext.sty 2000/06/29 v2.01
amsgen.sty 1999/11/30 v2.0
array.sty 2008/09/09 v2.4c Tabular extension package (FMi)
l3keys2e.sty 2014/11/25 v5471 LaTeX2e option processing using LaTeX3 keys
translator.sty 2010/06/12 ver 1.10
keyval.sty 1999/03/16 v1.13 key=value parser (DPC)
translator-language-mappings.tex
answers.sty 2014/08/24 v2.16 Production of solution sheets in LaTeX2e
verbatim.sty 2003/08/22 v1.5q LaTeX2e package for verbatim enhancements
amsthm.sty 2004/08/06 v2.20
graphicx.sty 1999/02/16 v1.0f Enhanced LaTeX Graphics (DPC,SPQR)
graphics.sty 2009/02/05 v1.0o Standard LaTeX Graphics (DPC,SPQR)
trig.sty 1999/03/16 v1.09 sin cos tan (DPC)
graphics.cfg 2007/01/18 v1.5 graphics configuration of teTeX/TeXLive
pdftex.def 2011/05/27 v0.06d Graphics/color for pdfTeX
infwarerr.sty 2010/04/08 v1.3 Providing info/warning/error messages (HO)
ltxcmds.sty 2011/11/09 v1.22 LaTeX kernel commands for general use (HO)
epstopdf.sty 2010/02/09 v2.5 Conversion with epstopdf on the fly (HO)
epstopdf-base.sty 2010/02/09 v2.5 Base part for package epstopdf
grfext.sty 2010/08/19 v1.1 Manage graphics extensions (HO)
kvdefinekeys.sty 2011/04/07 v1.3 Define keys (HO)
kvoptions.sty 2011/06/30 v3.11 Key value format for package options (HO)
kvsetkeys.sty 2012/04/25 v1.16 Key value parser (HO)
etexcmds.sty 2011/02/16 v1.5 Avoid name clashes with e-TeX commands (HO)
ifluatex.sty 2010/03/01 v1.3 Provides the ifluatex switch (HO)
pdftexcmds.sty 2011/11/29 v0.20 Utility functions of pdfTeX for LuaTeX (HO)
ifpdf.sty 2011/01/30 v2.3 Provides the ifpdf switch (HO)
caption.sty 2013/05/02 v3.3-89 Customizing captions (AR)
caption3.sty 2013/05/02 v1.6-88 caption3 kernel (AR)
mhchem.sty 2015/04/07 v4.00 for typesetting chemical formulae
l3regex.sty 2014/11/25 v5471 L3 Experimental regular expressions
l3tl-build.sty 2014/08/25 v5378 L3 Experimental token list construction
l3tl-analysis.sty 2014/05/06 v4745 L3 Experimental token lists analysis
l3str.sty 2014/11/25 v5471 L3 Experimental strings
l3flag.sty 2014/11/25 v5471 L3 Experimental flags
l3str-convert.sty 2014/06/03 v5028 L3 Experimental string encoding conversions
calc.sty 2007/08/22 v4.3 Infix arithmetic (KKT,FJ)
amsmath.sty 2013/01/14 v2.14 AMS math features
amsbsy.sty 1999/11/29 v1.2d
amsopn.sty 1999/12/14 v2.01 operator names
ifthen.sty 2001/05/26 v1.1c Standard LaTeX ifthen package (DPC)
float.sty 2001/11/08 v1.3d Float enhancements (AL)
placeins.sty 2005/04/18 v 2.2
pdfpages.sty 2015/04/15 v0.4w Insert pages of external PDF documents (AM)
eso-pic.sty 2013/10/06 v2.0d eso-pic (RN)
atbegshi.sty 2011/10/05 v1.16 At begin shipout hook (HO)
xcolor.sty 2007/01/21 v2.11 LaTeX color extensions (UK)
color.cfg 2007/01/18 v1.5 color configuration of teTeX/TeXLive
pppdftex.def 2015/04/15 v0.4w Pdfpages driver for pdfTeX (AM)
makeidx.sty 2000/03/29 v1.0m Standard LaTeX package
enumerate.sty 1999/03/05 v3.00 enumerate extensions (DPC)
xspace.sty 2009/10/20 v1.13 Space after command names (DPC,MH)
textgreek.sty 2011/10/09 v0.7 Greek symbols in text
lgrenc.def 2013/12/02 v0.11.2 LGR Greek font encoding definitions
greek-fontenc.def 2014/12/12 v0.12 Common Greek font encoding definitions
lgrcmr.fd 2013/09/01 v1.0 Greek European Computer Regular
translator-basic-dictionary-English.dict
siunitx-abbreviations.cfg 2015/01/21 v2.6e siunitx: Abbreviated units
supp-pdf.mkii
—-Correction—-
A double \usepackage{caption} removed (still the same error). File list updated (probably did not change).
—-Problem solved—-
I updated MikTeX and all packages; this solved the problem.
Best Answer
You are hitting an obscure bug in LaTeX prior to the 2015 kernel. I suspect the “new” machine has a non updated TeX distribution.
The best thing you can do is to ensure that the TeX distribution is the most recent one, with all updates in place.
There is a workaround, anyway: just define a new counter before the error happens.