The problem lies in the fact that you chose to create symbolic links for the executables in /usr/local/texlive/2011/bin/<architecture> to /usr/local/bin.
With tlmgr there's the possibility to update them, but the action is not performed automatically.
However, my advices are:
Always install the full TeX Live
Never create symbolic links, particularly on Debian based systems
If you don't have strict space constraints, do a full TeX Live install. It would have avoided the problem of installing the XeTeX subsystem.
Changing what's in /usr/local/bin is dangerous as other system utilities may choose to install something there. It's better to change the PATH variable and the safest method is to write a file zzz-texlive.sh containing
export PATH=/usr/local/texlive/2011/bin/`uname -i`-linux:$PATH
export MANPATH=/usr/local/texlive/2011/texmf/doc/man:$MANPATH
export INFOPATH=/usr/local/texlive/2011/texmf/doc/info:$INFOPATH
unset TEXINPUTS
unset TEXMFCONFIG
and move it into /etc/profile.d. After a logout/login cycle, the PATH variable will contain the correct directory for the executables.
Update
The problem appears only with the edges. A possibility is to scale only the edges. Firstly we get the coordinates, then we divide them by 10 and finally we scale the coordinates by 10. I changed some styles from the original code.
\documentclass[onlymath]{beamer}
\usefonttheme{serif}
\usepackage[orientation=portrait,size=a0,scale=1.0]{beamerposter}
\usepackage{eulervm}
\usepackage{tikz}
\usetikzlibrary{shapes,arrows,positioning,matrix}
\begin{document}
\begin{frame}[t,fragile]{}
\begin{block}{Big TikZ Test}
\begin{center}
\begin{tikzpicture}[blk/.style= {rectangle,draw,text width=2in,text centered},
edge/.style = {draw =black!50 ,line width=3pt,->}]
\matrix[row sep=1cm,column sep=1cm] {%
\node[blk] (a) {A};
&
\node[blk] (b) {B};
&
\node[blk] (c) {C};
&
\node[blk] (d) {D};
&
\node[blk] (e) {E};
&
\node[blk] (f) {F};
&
\node[blk] (g) {G};
&
\node[blk] (h) {H};
&
\node[blk] (i) {I};
&
\node[blk] (j) {J};
\\
};
\path[edge] (j) edge [bend left=30] (i)
edge [bend left=30] (h)
edge [bend left=30] (g)
edge [bend left=30] (f)
edge [bend left=30] (e);
\path (a.south);
\pgfgetlastxy{\ax}{\ay}
\path (b.south);
\pgfgetlastxy{\bx}{\by}
\path (c.south);
\pgfgetlastxy{\cx}{\cy}
\path (d.south);
\pgfgetlastxy{\dx}{\dy}
\begin{scope} [scale=10]
\path[edge] (j) edge [bend left=30] (0.1*\dx,0.1*\dy)
edge [bend left=30] (0.1*\cx,0.1*\cy)
edge [bend left=30] (0.1*\bx,0.1*\by)
edge [bend left=30] (0.1*\ax,0.1*\ay);
\end{scope}
\end{tikzpicture}
\end{center}
\end{block}
\end{frame}
\end{document}
There is another problem, when we crate the edges, in the log I see
Missing character: There is no ï in font nullfont!
Missing character: There is no ¿ in font nullfont!
Missing character: There is no ¼ in font nullfont!
Missing character: There is no ï in font nullfont!
Missing character: There is no ¿ in font nullfont!
Missing character: There is no ¼ in font nullfont!
Missing character: There is no ï in font nullfont!
Missing character: There is no ¿ in font nullfont!
Missing character: There is no ¼ in font nullfont!
One warning for one edge
update 2
Perhaps it's a bug in 'to'. I try with controls and the code compiles without errors. I used some control points but without calculations.
\begin{tikzpicture}[blk/.style= {rectangle,draw,text width=2in,text centered},
edge/.style = {draw =black!50 ,line width=3pt,->}]
\matrix[row sep=1cm,column sep=1cm] {%
\node[blk] (a) {A};
&
\node[blk] (b) {B};
&
\node[blk] (c) {C};
&
\node[blk] (d) {D};
&
\node[blk] (e) {E};
&
\node[blk] (f) {F};
&
\node[blk] (g) {G};
&
\node[blk] (h) {H};
&
\node[blk] (i) {I};
&
\node[blk] (j) {J};
\\
};
\path[edge] (j) edge [bend left=30] (i)
edge [bend left=30] (h)
edge [bend left=30] (g)
edge [bend left=30] (f)
edge [bend left=30] (e);
\path[edge] (j) .. controls ([{shift=(210:20)}]j) and ([{shift=(-30:20)}]d) .. (d);
\path[edge] (j) .. controls ([{shift=(210:25)}]j) and ([{shift=(-30:25)}]c) .. (c);
\path[edge] (j) .. controls ([{shift=(210:30)}]j) and ([{shift=(-30:30)}]b) .. (b);
\path[edge] (j) .. controls ([{shift=(210:35)}]j) and ([{shift=(-30:35)}]a) .. (a);
\end{tikzpicture}
Best Answer
Following the suggestion in How do I install an individual package on a Linux system?, you can search Debian's database to find the file
etoolbox.sty. The search for squeeze points to thetexlive-latex-extrapackage.