use \DeclareFixedFont instead of \newfont

[Ivo Pletikosić]

According to http://tex.stackexchange.com/questions/336002/how-to-reduce-the-size-of-the-chapter-numbers, one should not use \newfont in a LaTeX document. Thus

\ifthenelse{\boolean{@eulerchapternumbers}}% font for the chapter numbers
    {\DeclareFixedFont{\chapterNumber}{U}{eur}{b}{n}{70}}%
    {\DeclareFixedFont{\chapterNumber}{T1}{pplj}{m}{n}{70}}    

[André Miede]

Fixed in next release (4.4).