# [Tex/LaTex] Subcaption package error, even without the use of the subfigure package

floatssubcaptionsubfloats

I have read countless instructions on how to use the subcaption package, and tried several examples. Each time I get two types of errors, which I will post further down. This is my premable:

\documentclass[12pt, a4paper, oneside]{Thesis} % Paper size, default font size and one-    sided paper
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[american]{babel}
\usepackage{csquotes}
\DeclareUnicodeCharacter{00A0}{~}
\graphicspath{{./Figures/}} % Specifies the directory where pictures are stored
\usepackage[backend=bibtex, natbib, style=authoryear,maxbibnames=9, doi=false,    url=true, isbn=false]{biblatex}
\DeclareLanguageMapping{american}{american-apa}
\DefineBibliographyStrings{norsk}{bibliography = {References},}
\usepackage{hyperref}
\usepackage{pgfplots}
\pgfplotsset{compat=1.9}
\usepackage{float}
\usepackage{mdwlist}
\usepackage{chngcntr}
\usepackage{paralist}
\usepackage{soul}
\usepackage{caption}
\usepackage{subcaption}
\newcommand{\Qline}[1]{\noindent\rule{#1}{0.6pt}}


This is the current caption code:

\begin{figure}
\centering
\begin{subfigure}[b]{0.3\textwidth}
\includegraphics[width=\textwidth]{E:/Masteroppgaven/TeXhis/Figures/QuickRight}
\caption{Original Prototype}
\label{fig:QRight}
\end{subfigure}%
~
\begin{subfigure}[b]{0.3\textwidth}
\includegraphics[width=\textwidth]{E:/Masteroppgaven/TeXhis/Figures/QuickLeft}
\caption{Second Iteration}
\label{fig:QLeft}
\end{subfigure}
\caption{Quick Selection}\label{fig:QSelect}
\end{figure}


Finally, these are the error messages that I am given.

C:\Program Files (x86)\MiKTeX 2.9\tex\latex\caption\subcaption.sty:48:
Package subcaption Error: This package can't be used in cooperation [\endinput}{}]

E:\Masteroppgaven\TeXhis\Chapters\UseOfTheNovelDesignPrinciples.tex:28:
Missing number, treated as zero. [\begin{subfigure}[b]{0.3\textwidth}]

E:\Masteroppgaven\TeXhis\Chapters\UseOfTheNovelDesignPrinciples.tex:28:
Illegal unit of measure (pt inserted). [\begin{subfigure}[b]{0.3\textwidth}]


Does anyone have any idea of how I can solve this issue? The reason I added the preamble is that most other people have stated that the subcaption package can't be used together with the subfigure package, but as you can see I do not add it to my Thesis.tex

Seeing the error message, what happens is that your document class Thesis internally loads subfigure and this produces the clash, since subcaption and subfigure cannot be used simultaneously. Search the file Thesis.cls for a line
\RequirePackage{subfigure}