Instead of numbers, symbols are showing up in the references using biblatex

Question

I am using biblatex for creating a poster.I made a small example with all the packages I am using.

    \documentclass[]{beamer}
\usepackage[orientation=portrait,size=a0,scale=1,debug]{beamerposter}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage{amsmath}
\usepackage{csquotes}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{textcomp}
\usepackage[style=numeric-comp,maxcitenames=3,backend=bibtex,url=false,doi=false,isbn=false,hyperref=false,bibencoding=ascii]{biblatex}
\addbibresource{library.bib}
\usepackage{wasysym}
\usepackage{graphicx}
\usepackage{multirow}
\usepackage[document]{ragged2e}
\usepackage[version=3]{mhchem}
\usepackage{multicol}
\usepackage{fancyhdr}
\usepackage{tikz}
\usepackage{lmodern}
\usepackage[version=3]{mhchem}
\usepackage[lf]{venturis}
\usepackage[version-1-compatibility]{siunitx}
\renewcommand*{\bibfont}{\scriptsize}
\DeclareSIUnit\Molar{\textsc{m}}
\setbeamertemplate{caption}[numbered] 

\begin{document}

tedhjfshsofhewihewi\cite{Meyer1996a}nfoeeghraeoghru

\begin{minipage}{0.98\columnwidth}
    \begin{multicols}{3}
         \noindent
             %\scriptsize

                        %\setbeamertemplate{bibliography item}[text]
                %\bibliographystyle{abbrv}
                %\bibliography{library}
                \printbibliography
                %\vspace{3em}
        \end{multicols} 
            \end{minipage}

\end{document}

In principle everything is fine. No error messages and no bibtex related warnings. I get the (1) in the text. However in the reference list, instead of

(1) Author1, Title1, Journal1...

I get

Author1, Title1, Journal1

Any ideas? Thanks for your help.