I realised that in the exportation process from cnb to tex, there is a command trying to redefine the \author command
\newcommand{\author}[1]{{\bfseries #1}}
This is the 29th line of the exported tex file.
Since the \author command is already defined, the above line raises a warning. It should be changed to 
\renewcommand{\author}[1]{{\bfseries #1}}