Q:

How could I remove a header in a beamer presentation? 

I'm editing a theme beamer, but I have a trouble I would like to remove the header without remove neither footer or the lateral navigation bar.  I've tried with the follow option:
\defbeamertemplate*{headline}{split theme}
{

 %nothing  

} 

but when I try to compile I receive the follow error:
!  LaTeX Error: Command \beamer@@tmpop@headline@split theme already defined. 

I use theme PaloAlto.  I hope that somebody can help me. 
EDIT by Marco Daniel:
Here the solution presented as a minimal working example:
\documentclass{beamer}
\usetheme{PaloAlto}
\setbeamertemplate{headline}{}

\begin{document}
\section{foo}
\begin{frame}
\frametitle{bar}
Text
\end{frame}
\end{document}

A:

The solution is to use \setbeamertemplate{headline}{}.   This clears the "template" for the headline, ensuring that when the headline is typeset then nothing is done.   It is important to ensure that this is not overridden by other styles so should be placed in the preamble after any themes have been loaded. 
Example:
\documentclass{beamer}
\usetheme{PaloAlto}
\setbeamertemplate{headline}{}

\begin{document}
\section{foo}
\begin{frame}
\frametitle{bar}
Text
\end{frame}
\end{document}

This produces:

With the \setbeamertemplate command commented out then it produces:

(This was answered in the comments; I'm posting this to remove it from the "unanswered" queue.   As the real problem was due to a theme overriding the template, I considered having it closed as "too localised", but I also thought that this might be a common question and having the question closed with the answer in the comments is not the most helpful way to present this question and answer.   I've marked it CW partly as it's not my answer and partly so that others can easily improve it and know that they are encouraged to do so.)