Error on grouping level [closed]

Question

I'm trying to create a graph from a big file with pgfplots. This is the code I use:

\begin{figure}
\makebox[\textwidth][c]{
\subfloat[]
    {
    \tikzsetnextfilename{SJ_RK_1e4_1e10_(circular)_Energy-S}
    \begin{tikzpicture}
    \begin{axis}[title={Deux corps}, xlabel={$t$ (\si{\second})}, ylabel={$E_{\text{méc}}$ (\si{\joule})},%
    legend cell align=left]

        \addplot[blue,thick]
            table[x index=0,y index=3,each nth point={3}] {Data/SJ_RK_1e4_1e10_(circular)_Energy.dat};

        \legend{}
    \end{axis}
    \end{tikzpicture}} \quad

\subfloat[]
    {
    \tikzsetnextfilename{SJ_RK_1e4_1e10_(circular)_Energy-J}
    \begin{tikzpicture}
    \begin{axis}[title={Deux corps}, xlabel={$t$ (\si{\second})}, ylabel={$E_{\text{méc}}$ (\si{\joule})},%
    legend cell align=left]

        \addplot[blue,thick]
            table[x index=0,y index=6,each nth point={3}] {Data/SJ_RK_1e4_1e10_(circular)_Energy.dat};

        \legend{}
    \end{axis}
    \end{tikzpicture}}}

    \caption[Deux corps: énergie mécanique du Soleil en mouvement circulaire]{}\label{SJ_RK_1e4_1e10_(circular)_Energy-SJ}
\end{figure}

Unfortunately I obtains the following error, trying to compile the second graph (the first works well!):

! Package pgfplots Warning: Axis range for axis y is approximately empty; enlar
ging it.
! TeX capacity exceeded, sorry [grouping levels=255].
\pgfmath@basic@divide@ #1#2->\begingroup 
                                         \pgfmath@x =#1pt\relax \pgfmath@y =...
l.393   \end{tikzpicture}}}

Here is how much of TeX's memory you used:
 37753 strings out of 493488
 809240 string characters out of 3141326
 1690572 words of memory out of 3000000
 40374 multiletter control sequences out of 15000+200000
 69173 words of font info for 117 fonts, out of 3000000 for 9000
 957 hyphenation exceptions out of 8191
 361i,12n,477p,915b,4921s stack positions out of 5000i,500n,10000p,200000b,50000s

!  ==> Fatal error occurred, no output PDF file produced!

What kind of error is this? What I'm making wrong? Thank you.