# Error when using a block inside a frame in a beamer class document

The piece of code in question (I am using the "physics" package for bras and kets):

\begin{block}
\begin{equation*}
\ket{\psi_{n\bm{k}}} = \frac{1}{\sqrt{N}}\sum_{\bm{R}}e^{i\bm{k}\cdot\bm{R}}\ket{\phi_{n\bm{R}}}
\end{equation*}
\end{block}
\end{frame}


The errors I get:

physics.sti (error): Missing \endcsname inserted. \end{frame}
physics.sti (error): TeX capacity exceeded, sorry [input stack size=5000]. \end{frame}
physics.sti (warning): Font shape OT1/cmss/bx/it' undefined(Font) using OT1/cmss/bx/n' instead


I have the physics.tex and physics.sty file in the same folder as my tex file (and has always worked fine). I tried using different things instead of the "equation*" environment, but get the same errors. Any ideas?

\begin{block}{Title}