Beamer - ! File ended while scanning use of \next

The fix was 2-part

• \end{frame} can NOT be indented
• \end{frame} cannot have any comments directly after it

Changing this line fixed the error.

I got the same error message and the problem was a [fragile] in

\begin{frame}[fragile]{Title}
 ...
\end{frame}

that I use for frames that contain LaTeX Listings code. I put it there before actually using Listings in that frame.