Consider below MCWE:
\documentclass{memoir}
\usepackage{hyperref}
\hypersetup{colorlinks=true}
\hypersetup{linkcolor=[rgb]{0.2,0.4,0.7}}
\let\orgautoref\autoref
\providecommand{\Autoref}{\def{equationautorefname{Eq.}\orgautoref}
\renewcommand{\autoref}{\def\equationautorefname{eq.}\orgautoref}
\begin{document}
\frontmatter
\tableofcontents
\listoffigures
\mainmatter
\chapter{Bla}
\section{Bla}
\begin{figure}
\caption{\Autoref{bla} \autoref{bla}\label{fig}}
\end{figure}
\autoref{fig}
\begin{equation}
bla\label{bla}
\end{equation}
\chapter{Bloo}
\section{Bloo}
\begin{figure}
\caption{Bloo}
\end{figure}
\end{document}
If I comment out the \autoref redefinition above, everything works, but if I don't, a second run of pdflatex or latex gives this error:
! Missing control sequence inserted.
<inserted text>
\inaccessible
l.2 ...quation{eq.}\autoref {bla}}}{1}{figure.1.1}
Please don't say `\def cs{...}', say `\def\cs{...}'.
I've inserted an inaccessible control sequence so that your
definition will be completed without mixing me up too badly.
You can recover graciously from this error, if you're
careful; see exercise 27.2 in The TeXbook.
The culprit is the \listoffigures, and the error refers to the .lof file, which contains the following:
\addvspace {10pt}
\contentsline {figure}{\numberline {1.1}{\ignorespaces Bla \def Equation{eq.}\autoref {bla}}}{1}{figure.1.1}
\addvspace {10pt}
\contentsline {figure}{\numberline {2.1}{\ignorespaces Bloo}}{3}{figure.2.1}
which seems wrong to me: the \autorefequationname ("Equation") has already been expanded instead of the \def command being executed.
The documentclass doesn't really matter, it also occurs with e.g. book.
How can I solve this error? I have renamed all \autoref names and also introduced an \Autoref, so I really don't want to stop using it, unless there is no other way.

\def\equationautorefname{eq.}inside a\renewcommandfor\autoref. Why not just execute it by itself? – Mico Apr 01 '15 at 14:06\Autorefcommand (which was missing from my original example) won't work anymore (see updated code). By writing both like this, it magically works. I understand it's a bit of a hack, but I didn't find any other way of doing this. – rubenvb Apr 01 '15 at 14:22\caption's optional argument for a short caption, which is then placed in the list of figures instead. If I avoid\autorefthere, I should be fine. A better solution is still welcome though! – rubenvb Apr 01 '15 at 14:37cleverefpackage. Hope it works for you. For (much) more information about the cross-referencing capabilities of thehyperrefandcleverefpackages see, e.g., the posting Cross-reference packages: which to use, which conflict? – Mico Apr 01 '15 at 14:40\Autorefis fragile, it contains an assignment, thus\protect\Autorefis needed in moving arguments as in\caption. – Heiko Oberdiek Apr 01 '15 at 14:41