You can't use \spacefactor in vertical mode

Question

The following code returns the error message in the title

\usepackage{amsmath,amssymb}
    \usepackage{setspace}
    \begin{document}
      \begin{titlepage}%
            \noindent
            \includegraphics[viewport=8 8 185 55]{picture} \hfill
             \vspace{-6pt}
    \vspace{3cm}

    \let\footnotesize\small
    \let\footnoterule\relax
    \let \footnote \thanks

    \begin{center}
        \begin{spacing}{1.8}
          {\huge \bfseries \@title}
        \end{spacing}

        \large \@thesistype
    \end{center}

    \vspace{0.4cm}

    \begin{center}
        \large
        \@author

        \texttt{\small \@email}
    \end{center}%

    \vspace{0.4cm}

    \begin{center}
        \@institute
    \end{center}

    \vspace{1cm}

    \ifx \@logo \@empty
        \relax
    \else
    \begin{center}
        \@logo
    \end{center}
    \fi

    \vfill
    \begin{center}
        \textbf{Supervisors:} \\[2pt] \@supervisors
    \end{center}

    \vspace{0.2cm}

    \begin{center}
        \@date
    \end{center}

\end{titlepage}%
\end{document}

A very similar problem is discussed here: \@ title and You can't use `\spacefactor' in vertical mode However, I am too inexperienced to figure out what to do exactly. For example, I don't understand what command I am redefining that is so problematic. The incriminated line is {\huge \bfseries \@title}. Any easy fixes for this?