Error when trying to use the subcaption package

Error when trying to use the subcaption package

When I try to use the subcaption package (\usepackage{subcaption}), I get
some errors. However, using the subfigure package
(\usepackage{subfigure}), the compilation is successful with no errors. I
cannot figure out what is wrong...
here is a code example:
\documentclass[12pt, a4paper, oneside]{book}
\usepackage{fullpage}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{graphicx}
\usepackage{alltt}
\usepackage{latexsym}
\usepackage{exscale}
\usepackage[numbers, sort&compress]{natbib}
\usepackage{rotating}
\usepackage{changepage}
%\usepackage{notoccite}
%a useful package if you write url addresses:
%\usepackage{url}
\usepackage[labelfont=bf]{caption}
\usepackage{subcaption}
\usepackage{epsfig}
\begin{document}
\begin{figure}[htb]
\centering
\subfigure[]
{
\label{fig: Image1}
\includegraphics[width=76mm,height=60mm]{CordicStruc.pdf}
}
\subfigure[]
{
\label{fig: Image2}
\includegraphics[width=76mm,height=60mm]{Diagram1.pdf}
}
\caption{\textbf{(a) Block diagram of floating-
point CORDIC co-processor architecture.} \textbf{(b) Pre-Process module in
CORDIC co-processor.}}
\end{figure}
\end{document}