Illegal parameter number in definition of \enit@before. You meant to type ## instead of #, right?

Question

I am trying to renew the \item command, inside the \setlist command for How to create a enumerate list adding a custom prefix before each item number?, but latex keeps telling me:

test1.tex:22: Illegal parameter number in definition of \enit@before
You meant to type ## instead of #, right?
Or maybe a } was forgotten somewhere earlier, and things
are all screwed up? I'm going to assume that you meant ##.

But I am already typing ##. I also tried typing ###, #### and #####, but the error still the same. If I replace the ## by a single one #, then, latex stops creating the PDF correctly. As it is now, the PDF is generated correctly, even with that error popping up.

\documentclass{scrbook}
\usepackage{enumitem}
\usepackage{xspace}

\newcounter{descriptcount}
\newlist{enumdescript}{description}{1}

\setlist[enumdescript,1]{%
  before={%
    \setcounter{descriptcount}{0}%
    \renewcommand*\thedescriptcount{\arabic{descriptcount}}%
    \let\olditem\item%
    \renewcommand{\item}[1][]{%
       \olditem##1\space\stepcounter{descriptcount}\thedescriptcount)\xspace}%
  },
  after={\let\item\olditem},
  align=left
}

\begin{document}
\begin{enumdescript}
   \item one
   \item two
   \item[Some Text] three
   \item four
   \item five
\end{enumdescript}
\end{document}

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Answer 1

With these keys it is sometimes hard to guess at which level one is, so I suggest to use

\documentclass{scrbook}
\usepackage{enumitem}
\usepackage{xspace}

\newcounter{descriptcount}
\newlist{enumdescript}{description}{1}

\def\renewitem{%
  \setcounter{descriptcount}{0}%
  \renewcommand*\thedescriptcount{\arabic{descriptcount}}%
  \let\olditem\item%
  \renewcommand{\item}[1][]{%
    \olditem##1\space\stepcounter{descriptcount}\thedescriptcount)\xspace%
  }%
}
\setlist[enumdescript,1]{%
  before={\renewitem},
  after={\let\item\olditem},
  align=left,
}

\begin{document}
\begin{enumdescript}
   \item one
   \item two
   \item[Some Text] three
   \item four
   \item five
\end{enumdescript}
\end{document}