siunitx with svg graphics

Question

I am using pdfLaTeX (TeX Live 2011) to compile a document. Unfortunately it does not compile. Again, my example compiles flawlessly with TeX Live 2009. I include an SVG/PDF graphics following this guide. To do so I first create a drawing in an SVG file, then I export it to PDF and pdf_tex files.

In the SVG file I added a line of text like this:

\SI{6}{\arcsecond}

The figure is included by:

\begin{figure}[htbp]
\centering
\def \svgwidth{\columnwidth}
\includesvg{path-to-figure}
\caption{\SI{6}{\metre}}
\label{fig:label-of-figure}
\end{figure}

The \includesvg command is defined as:

\newcommand{\executeiffilenewer}[3]{% 
  \ifnum\pdfstrcmp{\pdffilemoddate{#1}}% 
  {\pdffilemoddate{#2}}>0% 
    {\immediate\write18{#3}}\fi%
} 
\newcommand{\includesvg}[1]{%
\executeiffilenewer{#1.svg}{#1.pdf}{% 
inkscape -z -D --file=#1.svg %
--export-pdf=#1.pdf --export-latex}%
\input{#1.pdf_tex}%
}

Parts of the generated pdf_tex file.

\begin{picture}(1,0.44809873)%
    \put(0,0){\includegraphics[width=\unitlength]{snifs_fov.pdf}}%
    \put(0.47868192,0.06651686){\color[rgb]{0,0,0}\makebox(0,0)[lb]{\smash{c) foo + bar + baz }}}%
    \put(0.47868192,0.17904892){\color[rgb]{0,0,0}\makebox(0,0)[lb]{\smash{b) bar + baz }}}%
    \put(0.47868192,0.33397134){\color[rgb]{0,0,0}\makebox(0,0)[lb]{\smash{a) baz}}}%
    \put(0.01018567,0.21107977){\color[rgb]{0,0,0}\makebox(0,0)[lb]{\smash{\SI{6}{\arcsecond}}}}%
  \end{picture}%
\endgroup%

This is the resulting error.

(./figs/graphics/snifs_fov.pdf_tex
<./figs/graphics/snifs_fov.pdf, id=104, 376.15532pt x 168.55472pt>
<use ./figs/graphics/snifs_fov.pdf>)
! Undefined control sequence.
\arcsecond ->\ERROR 

UPDATE: I have mistakenly considered the SVG file to be the root of the error. In fact the same text, which is in the SVG file, follows in a paragraph after the figure. I debugged this by changing the text in the SVG file. The error message after compilation did not change. And also JosephWright's confirmation, that it is possible to compile the file in an MWE, helped me to find out.

Answer 1

(More of a comment, but too long.) For me, using

\documentclass{article}
\listfiles
\usepackage{siunitx,graphicx}
\newcommand{\executeiffilenewer}[3]{% 
  \ifnum\pdfstrcmp{\pdffilemoddate{#1}}% 
  {\pdffilemoddate{#2}}>0% 
    {\immediate\write18{#3}}\fi%
} 
\newcommand{\includesvg}[1]{%
%\executeiffilenewer{#1.svg}{#1.pdf}{% 
%inkscape -z -D --file=#1.svg %
%--export-pdf=#1.pdf --export-latex}%
\input{#1.pdf_tex}%
}
\begin{document}
\begin{figure}
  \includesvg{snifs_fov}
\end{figure}
\end{document}

and a .pdf_tex file created using Inkscape works fine (I don't have it on my path, so did the conversion in the GUI). Works with both siunitx v2.5c and latest release.