
Was ist da falsch?
\usepackage{fancyhdr}
\pagestyle{fancy}
\setlength{\headheight}{25pt}
\fancyhead{}
\fancyfoot{}
\fancyhead[EL,OR]{\nouppercase{\leftmark}}
\renewcommand{\headrulewidth}{0.1pt}
\renewcommand{\footrulewidth}{0.1pt}
\fancypagestyle{plain}{%
\fancyhf{}%
\renewcommand{\headrulewidth}{0pt}
\renewcommand{\footrulewidth}{0pt}}
\fancyfoot[EL,OR]{\thepage}

