I use MiKTeX 2.9 and `tikz` package and use TeXworks to make simple figures, these are saved in pdf file by pdfLaTeX. I wish to have them as EPS file. I read here:
[Export eps figures from TikZ](https://tex.stackexchange.com/questions/8641/export-eps-figures-from-tikz)
I use a simple example 

```
\documentclass{article}
\usepackage{tikz}

% set up externalization
\usetikzlibrary{external}
\tikzset{external/system call={latex \tikzexternalcheckshellescape -halt-on-error
-interaction=batchmode -jobname "\image" "\texsource" && 
dvips -o "\image".ps "\image".dvi &&
ps2eps "\image.ps"}}
\tikzexternalize[shell escape=-enable-write18] % MikTeX uses a -enable-write18 instead of --shell-escape.

\begin{document}
\begin{tikzpicture}
\draw (0,0) circle (1cm);
\end{tikzpicture}
\end{document}

```

and get the following error:

```
===== 'mode=convert with system call': Invoking 'latex -halt-on-error -interact
ion=batchmode -jobname "untitled-1-figure0" "\def\tikzexternalrealjob{untitled-
1}\input{untitled-1}" && dvips -o "untitled-1-figure0".ps "untitled-1-figure0".
dvi && ps2eps "untitled-1-figure0.ps"' ========

! Package tikz Error: Sorry, the system call 'latex -halt-on-error -interaction
=batchmode -jobname "untitled-1-figure0" "\def\tikzexternalrealjob{untitled-1}    input{untitled-1}" && dvips -o "untitled-1-figure0".ps "untitled-1-figure0".dvi
 && ps2eps "untitled-1-figure0.ps"' did NOT result in a usable output file 'unt
itled-1-figure0' (expected one of .pdf:.jpg:.jpeg:.png:). Please verify that yo
u have enabled system calls. For pdflatex, this is 'pdflatex -shell-escape'. So
metimes it is also named 'write 18' or something like that. Or maybe the comman
d simply failed? Error messages can be found in 'untitled-1-figure0.log'. If yo
u continue now, I'll try to typeset the picture.

See the tikz package documentation for explanation.
Type  H <return>  for immediate help.
 ...                                              

l.15 \end{tikzpicture}  

```

I see many have got the same error. I do not know what to do. Can somebody please help?