I read here that if I want to automatically adjust capitalization for titles, I could use
\DeclareFieldFormat[article]{titlecase}{\MakeSentenceCase{#1}}. However this breaks compilation.
Here is a somewhat minimal example
\documentclass{article}
\usepackage{biblatex}
\usepackage{accents}
\DeclareFieldFormat[article]{titlecase}{\MakeSentenceCase{#1}} %%% <- offending line
\usepackage{filecontents}
\begin{filecontents}{test.bib}
@article{A01,
author = {Author, A.},
year = {2001},
title = {Alpha: {$Q_t=H\left(\underaccent{\leftarrow}S,\underaccent{\leftarrow}R,\Delta_t\right)A$}},
journaltitle = {Some journ.}
}
\end{filecontents}
\addbibresource{test.bib}
\begin{document}
Can it survive titlecase \autocite{A01}?
\printbibliography
\end{document}
PDF is not produced at all with offending line uncommented.
EDIT 6/8/2014
What a gaffe. I made a typo while I was moving things around. I had both lines, but I guess I was confused while making a minimal example. Original code still produces some "abstract" error Undefined control sequence and an error like Illegal parameter number in definition of \@tempa. I'd like to "suspend" this question till I clarify the situation. I suspect it is because of math in title, also it is contained within {}.
EDIT 6/9/2014
I updated the sample code. It compiles okay as is unless I uncomment that line with titlecase. Note that math is contained within curly braces.
EDIT 6/10/2014
Example was made lean and mean without unnecessary stuff as per request in comments.

titlefortitlecase? You are not using the declaration specified in the answer you linked to. – cfr Jun 08 '14 at 23:54\DeclareFieldFormat[article]{titlecase}{\MakeSentenceCase*{#1}}instead. (I just realised that that is the suggestion in the answer you linked to, why did you change that? You can still have\DeclareFieldFormat[article]{title}{#1}to get rid of the quotation marks.) – moewe Jun 09 '14 at 05:38\MakeSentenceCaseshould be fine with maths - especially if it is escaped in braces (you will want to escape your maths otherwise the formulae will be converted to sentence case as well and mayhem will ensue). The error "Illegal parameter number in definition of \@tempa" is very hard to investigate without an actual case where it occurs. – moewe Jun 09 '14 at 07:30accent's\underaccentis too much for\MakeSentenceCaseto cope. Even escaping does not seem to help. – moewe Jun 09 '14 at 17:58.bibentries and redefinitions of macros likedate+extrayearand changes of bibstrings. – moewe Jun 10 '14 at 05:56