I have a two column document in which I display a lot of figures. I also have to display some figures spanning the two columns.
To display "normal" figures I use this piece of code, for example:
\documentclass[conference]{IEEEtran}
\usepackage{subfig}
\usepackage{fixltx2e}
\usepackage{stfloats}
\begin{document}
\begin{figure}[!htb]
\centering
\subfloat[]{\includegraphics[width=0.49\linewidth]{figs/Case1/potential1_sd}} \hfill
\subfloat[]{\includegraphics[width=0.49\linewidth]{figs/Case1/potential2_sd}} \hfill
\subfloat[]{\includegraphics[width=\linewidth]{figs/Case1/sd_colorbar}}
\caption{}
\label{fig:case1_sd}
\end{figure}
\end{document}
To span a figure in two columns:
\begin{figure*}
\centering
\subfloat[]{\includegraphics[width=0.32\textwidth]{figs/Case1/potential1_feat}} \hfill
\subfloat[]{\includegraphics[width=0.32\textwidth]{figs/Case1/potential2_feat}} \hfill
\subfloat[]{\includegraphics[width=0.32\textwidth]{figs/Case1/sd_colorbar}}
\caption{}
\label{fig:case1_feat}
\end{figure*}
EDIT:
The problem seems to be happening with this piece of code:
\begin{figure*}
\subfloat[Vector Field]{\includegraphics[width=.2\textwidth]{figs/Case1/quiver_vector_field}} \hfill
\subfloat[Curl-free Component]{\includegraphics[width=.2\textwidth]{figs/Case1/quiver_rotational_free}} \hfill
\subfloat[Divergence-free Component]{\includegraphics[width=.2\textwidth]{figs/Case1/quiver_divergence_free}} \hfill
\subfloat[Harmonic]{\includegraphics[width=.2\textwidth]{figs/Case1/quiver_harmonic}} \\
% If I comment this line, everything works. Can't I use two rows too?
\subfloat[]{\includegraphics[width=.5\textwidth]{figs/Case1/quiver_colorbar}}
\caption{Mean vector fields. The color bar represents the vectors magnitudes.}
\label{fig:case1_meanvecs}
\end{figure*}
If I commented it, the others figures, including two column figures displayed with the code above, can be seen in the document.
However, when I enable the second piece of code, all figures in my .tex disappear. I lose references, everything. I don't know what I'm doing wrong.
Thank you in advance.

0.32\textwidthto, say,0.3\textwidth? Incidentally, since the subfigures jointly span the width of either a column or the full text block,\centeringisn't needed in either case. – Mico Sep 02 '14 at 19:45[!htb]omitspso makes it quite hard to position the float and makes it more likely that all floats go to the end of the document. Also, habitually using!is odd: it says to ignore the default constraints, so if you always do that it is better to simply change the specified constraints. – David Carlisle Sep 02 '14 at 20:17