figure, errors '\undefined control sequence - \ltx@Ifundefined{…'

Question

Please help me tell why the following code is not correct?

\documentclass[a4paper,12pt]{article}
\usepackage{graphicx}
\begin{document}
\begin{figure}[htp]
\centering
\includegraphics[width=100mm]{lls.eps}
\hfill
\includegraphics[width=100mm]{AIC.eps}\\
\hfill
\includegraphics[width=100mm]{BIC.eps}\\
\end{figure}
\end{document} 

or other code:

\documentclass[a4paper,12pt]{article}
\usepackage{graphicx}
%\usepackage{subfig}
\begin{document}
\begin{figure}
  \centering
  \label{figur}\caption{equation...}
  \begin{tabular}{cp{2cm}c}
    \includegraphics[width=60mm]{1.eps}& & \includegraphics[width=60mm]{lls.eps}\\
    & & &\\
    \includegraphics[width=60mm]{2.eps}& & \includegraphics[width=60mm]{AIC.eps}\\
    & & &\\
    \includegraphics[width=60mm]{3.eps}& & \includegraphics[width=60mm]{BIC.eps}\\
  \end{tabular}
\end{figure}
\end{document}

Answer 1

Your code is compilable, so there's no problem visible in those two examples.

Regarding the error message in the title: I recommend to install or to update the oberdiek bundle. This bundle contains a package ltxcmds.sty, which defines the macro \ltx@IfUndefined. I guess a package you're using relies on a current version of oberdiek and ltxcmds, respectively.