[pstricks] Problem with Seminar

[Eftaxiopoulos Dimitrios]

All seminar demo files compliled successfully, apart from sem-dem6.tex. I get 
an error related to \PstGaussPolygon in the following text

---------------------------------------------------------------------------------------------------------------------------------------------------------
\begingroup
\renewcommand{\slidestretch}{0.7} % To compress the lines for the caption
\begin{slide}
  \vspace*{-2mm}
  \slideheading{Building of a regular polygon of seventeen sides}
  \ifx\SeminarPaperVersion\AnswerYes
  \else
    \vspace{5mm}
  \fi
  \begin{figure}[htbp]
    \centering
    \psset{unit=0.5}%
    \PstGaussPolygon
    \caption{Building of a regular polygon of seventeen sides, according to
             the method introduced by Carl Friedrich \textsc{Gauss}.\newline
             This code is from Dominique \textsc{Rodriguez}, part of the
             examples of his `pst-eucl' PSTricks package for Euclidian
             geometry.}
  \end{figure}
\end{slide}
\endgroup
-------------------------------------------------------------------------------------------------------------------------------------------------
and a relative part of the error output is the following
-------------------------------------------------------------------------------------------------------------------------------------------------
[]

Overfull \hbox (389.93294pt too wide) detected at line 1150
[]
! Missing $ inserted.
 
                $
l.1150     \PstGaussPolygon
                           
! Extra }, or forgotten $.
 ...=1.5em},CodeFig=false]{O}{P_1}{PP_1}
                                                  \ncline [linestyle=solid]
{...
l.1150     \PstGaussPolygon
                           
! Missing $ inserted.
 
                $
l.1150     \PstGaussPolygon
                           
! Missing } inserted.
 
                }
l.1150     \PstGaussPolygon
---------------------------------------------------------------------------------------------------------------------------------------------------- 

Thanks
Dimitris