# Error in compiling pdf in bookdown

Hi all,
I have a rbookdown project for a students lab documentation. I generated it with rbookdown with 6 chapters and compiled it to get a pdf and keep the latex file. Finally I only added my specific latex header for the fine tuning of the formating. Everything went fine when I did this last year. Now I updated the book and when I try to compile the book I get:

output file: manual.knit.md
! Undefined control sequence.
l.22 \select@language
{english}

Error: LaTeX failed to compile manual.tex

I checked the log file but ther eis no more inforamtion about the error included. When I check the generated latex file it looks ok, but all cross-references in the document are not converted to latex, but are still in the markdown format: "@ref(fig:xxx).
Any suggestions are welcome.
Thanks
Alex

Can you share your files or a reproducible example ?

This usually mean there is a Tex package necesary where the command has been defined. Here it concerns language so maybe babel.

Have you tried update the latex packages ?

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