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Below is a minimalized template I have been using without any trouble for quite some time. It no longer runs on my system. I do not know if it's a problem with the xsim package, with one of its dependencies or just some weird local issue that should not be happening. I have updated my texlive installation. I'm on MacOS High Sierra. I am compiling with pdflatex Any ideas?

The error message I get:

I can't write on file `aux/xsim-stackoverflow-4-question-1-exercise-body.tex'. ...stion}[ID={Q001}, points={10}, tags={easy}]

I last successfully ran the code on 16 January 2019. I need a solution or workaround within a week (gasp!).

documentclass{article}

usepackage{filecontents}

begin{filecontents*}{QuestionBank.tex}

begin{question}[ID={Q001}, points={10}, tags={easy}]

First Question: Select one of the following solutions:

begin{enumerate}

item A

item B

item C

end{enumerate}

end{question}

begin{answer}

Solution to First Question

end{answer}

end{filecontents*}



usepackage{xsim}

usepackage[most]{tcolorbox}

xsimsetup{

  clear-aux,

  path = {aux}, % default path empty 

}



newcommand*includeQuestion[1]{%

  XSIMexpandcode{printexercise{question}{GetExerciseIdForProperty{ID}{#1}}}%

}



newcommand*includeSolution[1]{%

  XSIMexpandcode{printsolution{question}{GetExerciseIdForProperty{ID}{#1}}}%

}





DeclareExerciseEnvironmentTemplate{tcb}

{%

    tcolorbox[breakable,

        drop shadow,

        beforeafter skip = 1baselineskip,

        fonttitle   = bfseries,

        fontupper = normalsize,

        valign = top,

        colframe = IfInsideSolutionF{green!20!white}IfInsideSolutionT{blue!20!white},

        colback = IfInsideSolutionF{green!3!white}IfInsideSolutionT{blue!3!white},

        coltext = black,

        coltitle = black,

        boxrule = 1pt,

        width = linewidth,

        left = 2mm,

        title =

        IfInsideSolutionT{XSIMmixedcase{XSIMtranslate{solution}}~to~}%

        XSIMmixedcase{XSIMtranslate{question}}~GetExerciseProperty{counter}%

        IfInsideSolutionF{IfExercisePropertySetT{tags}{textbf{~~[ListExerciseTags{tags}{, }]}}}%

        IfInsideSolutionF{%

            GetExercisePropertyT{points}{%

                hfill[PropertyValue

                IfExerciseGoalSingularTF{points}

                    {XSIMtranslate{point}}~%

                    {XSIMtranslate{points}}]%

            }%

        }%

    ]%

    IfInsideSolutionT{}

}{endtcolorbox}



DeclareExerciseType{question}{

      exercise-env = question,

    solution-env = answer,

      exercise-name = question, % used with headings=true

    solution-name = solution,  % used with headings=true

      exercise-template = tcb,

    solution-template = tcb,

    counter = question,

}



DeclareExerciseCollection{myCollection}





begin{document}



collectexercises{myCollection}

input{QuestionBank.tex}

collectexercisesstop{myCollection}



includeQuestion{Q001}

includeSolution{Q001}



end{document}