Ho provato a fare come mi dicevi tu ma non è cambiato nulla.
Qui sotto il mio preambolo.
`\documentclass[a4paper,12pt]{book}
\usepackage[italian]{babel}
\usepackage{lipsum}
\usepackage{subfigure}
\usepackage{array}
\usepackage{booktabs}
\usepackage{longtable}
\usepackage{afterpage}
%\usepackage{graphicx}
\usepackage[pscoord]{eso-pic}
\setcounter{tocdepth}{3}
\setcounter{secnumdepth}{3}
\usepackage[latin1]{inputenc}
\usepackage{fancyhdr}
\usepackage{amsmath}
\usepackage[dvips]{graphicx}
\usepackage[hyperindex]{hyperref}
\hypersetup{bookmarks=true, pdfpagemode=UseOutlines}
\hypersetup{colorlinks=true,linkcolor=blue}
\usepackage{lscape}
\linespread{1.2} %interlinea
\setlength\headheight{15pt}
\newlength{\colwd}
\settowidth{\colwd}{\footnotesize Differenziazione}
\pagestyle{fancy}\addtolength{\headwidth}{20pt}
\renewcommand{\chaptermark}[1]{\markboth{\thechapter.\ #1}{}}
\renewcommand{\sectionmark}[1]{\markright{\thesection \ #1}{}}
\cfoot{} % nessun piede centrale di pagina (fa parte di fancyhdr)
\rhead[\fancyplain{}{\bfseries\leftmark}]{\fancyplain{}{\bfseries\thepage}}
\lhead[\fancyplain{}{\bfseries\thepage}]{\fancyplain{}{\bfseries\rightmark}}
`