Error message - possibly due to bibliography

Question

I am writing a report (I apologise for the coding being a little messy - I am new to using LaTeX and the report is a mix of two different templates) using Overleaf and JabRef and one error keeps coming up. I have googled the problem, but that didn't help. A friend has suggested, it might have something to do with the bibliography, but I cannot seem to find the error. The following error message shows (and it doesn't say where the error is, as it usually does):

[0] Config.pm:343> INFO - This is Biber 2.5
[0] Config.pm:346> INFO - Logfile is 'main.blg'
[40] biber:290> INFO - === Sun May 20, 2018, 10:29:32
[169] Utils.pm:165> ERROR - main.bcf is malformed, last biblatex run probably failed. Deleted main.bbl
[169] Biber.pm:113> INFO - ERRORS: 1

I am desperate for some help figuring out where I made an error and what the error message means. Can anyone spot the mistake(s)?

My main.tex looks like this:

\input{setup/preamble.tex}

\begin{document}

\pagestyle{empty} 
\pagenumbering{roman} 
\input{sections/01_forside.tex}
\input{sections/02_resume.tex}
\pagestyle{fancy}
\tableofcontents

%mainmatter
\pagenumbering{arabic}
\input{sections/03_projektformulering.tex}
\input{sections/04_luftmaengder.tex}
\input{sections/05_myndighedskrav.tex}
\input{sections/06_ventilation.tex}
\input{sections/07_konklusion.tex}
\printbibliography

%Tegninger (Drawings)
\renewcommand\appendixname{Tegninger}
\renewcommand\appendixpagename{Tegninger}
\renewcommand\appendixtocname{Tegninger}
\appendix
\appendixpage
\addappheadtotoc
\renewcommand\thechapter{\arabic{chapter}}
\input{sections/08_tegninger.tex}

%Appendiks (Appendix)
\renewcommand\appendixname{Appendiks}
\renewcommand\appendixpagename{Appendiks}
\renewcommand\appendixtocname{Appendiks}
\appendix
\appendixpage
\addappheadtotoc
\input{sections/09_appendiks.tex}

%Bilag (Annex)
\renewcommand\appendixname{Bilag}
\renewcommand\appendixpagename{Bilag}
\renewcommand\appendixtocname{Bilag}
\appendix
\appendixpage
\addappheadtotoc
\renewcommand\thechapter{\Roman{chapter}}
\input{sections/10_bilag.tex}

\end{document}

This is what my preamble.tex looks like:

\documentclass[11pt,a4paper]{report}

\usepackage[utf8]{inputenc}

\usepackage[english,danish]{babel}

\usepackage[sc]{mathpazo}
\linespread{1.05}

\usepackage[T1]{fontenc}

\usepackage{xcolor}
\definecolor{aaublue}{RGB}{33,26,82}% dark blue

\usepackage{graphicx}
\usepackage{pdfpages}

\usepackage{caption}
\captionsetup{%
  font=footnotesize,
  labelfont=bf 
}

\usepackage{array,booktabs}
\usepackage{array}
\setlength\extrarowheight{2pt}

\usepackage{framed}
\usepackage{dcolumn}

\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{textcomp}
\mathcode`\*="8000
{\catcode`\*\active\gdef*{\cdot}}

\usepackage{longtable}

\usepackage{amssymb}

\usepackage[framed,amsmath,thmmarks]{ntheorem}

\usepackage{tikz}
\usepackage{pgfplots}

\usepackage{titlesec}
\titleformat{\chapter}[display]{\normalfont\huge\bfseries}{\chaptertitlename\ \thechapter}{20pt}{\Huge}
\titleformat*{\section}{\normalfont\Large\bfseries}
\titleformat*{\subsection}{\normalfont\large\bfseries}
\titleformat*{\subsubsection}{\normalfont\normalsize\bfseries}
%\titleformat*{\paragraph}{\normalfont\normalsize\bfseries}
%\titleformat*{\subparagraph}{\normalfont\normalsize\bfseries}

\usepackage{float}

\usepackage{pdfpages}

\usepackage{titlesec}
\titleformat{\chapter}[block]
  {\normalfont\huge\bfseries}{\thechapter.}{1em}{\Huge}
\titlespacing*{\chapter}{0pt}{-19pt}{0pt}

\usepackage{appendix}

\usepackage{fancyhdr}
\setlength{\headheight}{15.2pt}
\pagestyle{fancy}
\fancyhf{}
\renewcommand{\headrulewidth}{0pt}
\lhead{\korttitel}
\cfoot{\thepage}
\fancyhead[r]{\small\nouppercase\rightmark}

\raggedbottom

\usepackage{calc}

\newcommand{\dato}{31. maj 2018}
\newcommand{\titel}{Kursusprojekt - Ventilation \& Indeklima}
\newcommand{\korttitel}{Kursusprojekt}
\newcommand{\gruppe}{Gruppe 407}
\newcommand{\MDH}{Mads Dalsgård Hansen}
\newcommand{\MST}{Morten Søndergaard Thomsen}
\newcommand{\MSS}{Mikkel Schjerup Simested}
\newcommand{\CBS}{Cecilie Bossow Sørensen}

\usepackage[defernumbers=true]{biblatex}
\addbibresource{bib/litteraturliste.bib}
\usepackage{csquotes}

\usepackage[nottoc]{tocbibind}

\usepackage{lastpage}

\usepackage[
colorinlistoftodos,
textwidth=\marginparwidth,
textsize=scriptsize,
]{todonotes}

\usepackage{hyperref}
\hypersetup{%
    pdfpagelabels=true,%
    plainpages=false,%
    pdfauthor={Author(s)},%
    pdftitle={Title},%
    pdfsubject={Subject},%
    bookmarksnumbered=true,%
    colorlinks=false,%
    citecolor=black,%
    filecolor=black,%
    linkcolor=black,% 
    urlcolor=black,%
    pdfstartview=FitH%
   }

\usepackage{siunitx}
\sisetup{per-mode=symbol}
\mathcode`\*="8000
{\catcode`\*\active\gdef*{\cdot}}
\usepackage{textcomp}
\usepackage{gensymb}

\usepackage{lipsum}
\usepackage{pdfpages}
\usepackage{graphicx}
\usepackage{subcaption}
\graphicspath{{graphics/}}
\usepackage{float}

My bibliography (litteraturliste.bib) made with JAbRef looks like this:

% Encoding: UTF-8

@Book{danvak,
  title     = {Varme- og Klimateknik, Grundbog},
  publisher = {Danvak ApS},
  year      = {2013},
  editor    = {H. E. Hansen; P. Kjerulf-Jensen; Ole B. Stampe},
  edition   = {4. udgave},
}

@Book{sbi196,
  title     = {SBi Anvisning 196 - Indeklimahåndbogen},
  publisher = {Statens Byggeforskningsinstitut},
  year      = {2000},
  editor    = {Ole Valbjørn; Susse Laustsen; John Høwish; Ove Nielsen; Peter A. Nielsen},
  edition   = {2. udgave},
}

@Book{mwg,
  title     = {MWGs slides},
  publisher = {Syddansk Universitet},
  year      = {2018},
  author    = {Martin Winther-Gaasvig},
}

@Book{exhausto,
  title     = {Indeklimaklasser},
  publisher = {Exhausto},
  year      = {2018/05/11},
  editor    = {Exhausto},
  url       = {https://www.exhausto.dk/projektering/Learning%20-%20Skoleventilation/Design%20af%20system/Indoor%20climate%20class},
}

@Book{klimadebat,
  title     = {CO2-koncentration},
  publisher = {Klimadebat.dk},
  year      = {2018/05/11},
  editor    = {Klimadebat.dk},
  url       = {http://www.klimadebat.dk/grafer_co2_ppm.php},
}

@Book{denlilleblaa,
  title     = {Den lille blå om Ventilation},
  publisher = {Dansk Energi},
  year      = {2016},
  author    = {Claus M. Hvenegaard; Christian Drivsholm},
  editor    = {Jørn Borup Jensen; Dorte Lindholm; Ditte Mikkelsen},
  edition   = {3. udgave},
}

@Book{ventilationsteknik,
  title     = {Varme- og Klimateknik, Ventilationsteknik},
  publisher = {Danvak ApS},
  year      = {2000},
  author    = {Ole B. Stampe},
  edition   = {4. udgave},
}

@Comment{jabref-meta: databaseType:bibtex;}