Subcaption environment failed. All figures containing a subfigure crashing all of a sudden

Question

I am currently writing my thesis in LaTeX. Today, all of a sudden, LaTeX started crashing. All the figures which contain a subfigure (NOTE: I am using the subcaption package) started receiving the following error:

Illegal unit of measure (pt inserted). \begin{subfigure}[b]{0.4\textwidth}

Also receiving other errors such as:

Missing number, treated as zero. \begin{subfigure}[b]{0.4\textwidth}

and

\begin{figure} on input line 170 ended by \end{subfigure}. \end{subfigure}

Below is an example of the code I'm using to generate subfigures.

\begin{figure}[htbp!]  % h t b p ! H for positioning of floats
\begin{subfigure}[b]{0.5\textwidth}
    \includegraphics[width=\textwidth]{CRMBuffetPSD5deg00eta0600}
    \caption{$\alpha$ = 5.0 \dg}
    \label{subfig:CRMBuffetPSD5deg00}
\end{subfigure}
\begin{subfigure}[b]{0.5\textwidth}
    \includegraphics[width=\textwidth]{CRMBuffetPSD6deg00eta0600}
    \caption{$\alpha$ = 6.0 \dg}
    \label{subfig:CRMBuffetPSD6deg00}
\end{subfigure}
\begin{center}
\begin{subfigure}[b]{0.5\textwidth}
    \includegraphics[width=\textwidth]{CRMBuffetPSD6deg50eta0600}
    \caption{$\alpha$ = 6.5 \dg}
    \label{subfig:CRMBuffetPSD6deg50}
\end{subfigure}
\end{center}
\caption{Surface $C_{P}$ response at $\eta$ = 0.6, and various incidences}
\label{fig:CRMBuffetUnsteadyPSD}

\end{figure}

The code worked fine for a significant period of time, today whilst writing I started getting this error. Closing and reopening LaTeX does not fix the issue.

I looked online already and it seems that the only solution found so far was to use the subcaption environment which I already do. Any other tips that could help me start troubleshooting this?

Thanks.

EDIT: I am using the Cambridge PhD thesis template. EDIT: Error disappears when not using the thesis template anymore. This is undesirable though

Answer 1

The only way to produce these error messages I'm aware of is using the subfigure package as well, and ignoring the first error message. Example:

\documentclass{article}
\usepackage[demo]{graphics}

\usepackage{subfigure}
\usepackage{subcaption}

\begin{document}

\begin{figure}[htbp!]  % h t b p ! H for positioning of floats
\begin{subfigure}[b]{0.5\textwidth}
    \includegraphics[width=\textwidth]{CRMBuffetPSD5deg00eta0600}
    \caption{$\alpha$ = 5.0 \dg}
    \label{subfig:CRMBuffetPSD5deg00}
\end{subfigure}
\caption{Surface $C_{P}$ response at $\eta$ = 0.6, and various incidences}
\label{fig:CRMBuffetUnsteadyPSD}
\end{figure}

\end{document}

These are the error messages when trying to compile the document above:

! Package subcaption Error: This package can't be used in cooperation
(subcaption)                with the subfigure package.

 ...                                              

! Missing number, treated as zero.
 
                   }
l.10 \begin{subfigure}[b]{0.5\textwidth}

? 
! Illegal unit of measure (pt inserted).
 
                   }
l.10 \begin{subfigure}[b]{0.5\textwidth}

? 

Underfull \hbox (badness 10000) in paragraph at lines 10--10
[]\OT1/cmr/m/n/8 (a)
Runaway argument?
width=\textwidth ]{CRMBuffetPSD5deg00eta0600} \caption {$\alpha $ = 5\ETC.
! Paragraph ended before \Gin@iii was complete.
 
                   \par 
l.30 

? 

! LaTeX Error: \begin{subfigure} on input line 10 ended by \end{document}.

The solution is to decide which package to use, either the subfigure or the subcaption package, but not both. (Note: The subfigure package offers a different syntax.)

Since you are using a special document class: Maybe there was an update of this class and now the subfigure package is included within this class? Please take a look if the subfigure package is used by a look into the log file, e.g.:

(/home/axel/.miktex/texmfs/install/tex/latex/subfigure/subfigure.sty
Package: subfigure 2002/07/30 v2.1.4 subfigure package