Error(s) in re-building vignettes:
  ...
--- re-building ‘introduction.Rnw’ using Sweave
Error: processing vignette 'introduction.Rnw' failed with diagnostics:
Running 'texi2dvi' on 'introduction.tex' failed.
LaTeX errors:
! Paragraph ended before \@tempa was complete.
<to be read again> 
                   \par 
l.56 \par
         \end{center}
! Paragraph ended before \@tempa was complete.
<to be read again> 
                   \par 
l.83 \par
         \end{center}
! Paragraph ended before \@tempa was complete.
<to be read again> 
                   \par 
l.90 \par
         \end{center}
! Paragraph ended before \@tempa was complete.
<to be read again> 
                   \par 
l.112 \par
          \end{center}
! Paragraph ended before \@tempa was complete.
<to be read again> 
                   \par 
l.131 \par
          \end{center}
! Paragraph ended before \@tempa was complete.
<to be read again> 
                   \par 
l.141 \par
          \end{center}
! Paragraph ended before \@tempa was complete.
<to be read again> 
                   \par 
l.150 \par
          \end{center}
! LaTeX Error: \begin{center} on input line 148 ended by \end{enumerate}.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              
! Paragraph ended before \@tempa was complete.
<to be read again> 
                   \par 
l.173 \par
          \end{center}
! Paragraph ended before \@tempa was complete.
<to be read again> 
                   \par 
l.190 \par
          \end{center}
! Paragraph ended before \@tempa was complete.
<to be read again> 
                   \par 
l.198 \par
          \end{center}
! Paragraph ended before \@tempa was complete.
<to be read again> 
                   \par 
l.205 \par
          \end{center}
! Paragraph ended before \@tempa was complete.
<to be read again> 
                   \par 
l.225 \par
          \end{center}
! Paragraph ended before \@tempa was complete.
<to be read again> 
                   \par 
l.238 \par
          \end{center}
! LaTeX Error: \begin{center} on input line 236 ended by \end{document}.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              
--- failed re-building ‘introduction.Rnw’

SUMMARY: processing the following file failed:
  ‘introduction.Rnw’

Error: Vignette re-building failed.
Execution halted