Wenn ich alle groben Fehler in Deinem Beispiel beseitige, um es zumindest lauffähig zu machen:
\documentclass[10pt,unicode,a4paper]{moderncv}
\moderncvtheme[blue]{casual}
\usepackage[utf8]{inputenc}
\usepackage{ragged2e}
\usepackage[ngerman]{babel}
\usepackage{datetime}
\usepackage{pdfpages} %http://www.sascha-frank.com/Faq/include_pdf.html & http://mirrors.ctan.org/macros/latex/contrib/pdfpages/pdfpages.pdf
\usepackage[scale=0.8,top=3.0cm,bottom=3.0cm]{geometry} % scale widens the margins, top=1cm moves the whole up
%\usepackage{lipsum} % just for dummy text
\setlength{\hintscolumnwidth}{2.9cm}
\usepackage{array}
%\usepackage[includeheadfoot,left=3cm,right=3cm,top=3cm,bottom=3cm]{geometry}
\AtBeginDocument{\recomputelengths}
%CV-Name-Schriftgröße ändern:
\renewcommand*{\namefont}{\fontsize{26}{8}\mdseries\upshape}
% Quelle: http://tex.stackexchange.com/questions/128052/font-size-in-moderncv
% http://tex.stackexchange.com/questions/162568/how-to-change-date-format-to-german
\newdateformat{myformat}{\THEDAY{. }\monthname[\THEMONTH], \THEYEAR}
% begin of inserted 1st block http://tex.stackexchange.com/questions/231388/howto-insert-text-beside-of-the-portrait-in-moderncv-casual-style#answers-header
\makeatletter
\def\insertpersonalinformation#1{\def\@insertpersonalinformation{#1}}
% commands
\renewcommand*{\makecvtitle}{%
% recompute lengths (in case we are switching from letter to resume, or vice versa)
\recomputecvlengths%
% ensure footer with personal information
\makecvfoot%er
% optional picture
\newbox{\makecvtitlepicturebox}%
\savebox{\makecvtitlepicturebox}{%
\ifthenelse{\isundefined{\@photo}}%
{}%
{%
\setlength\fboxrule{\@photoframewidth}%
\ifdim\@photoframewidth=0pt%
\setlength{\fboxsep}{0pt}\fi%
{\color{color1}\framebox{\includegraphics[width=\@photowidth]{\@photo}}}}}%
\usebox{\makecvtitlepicturebox}%
% name
\@initializelength{\makecvtitlepicturewidth}%
\settowidth{\makecvtitlepicturewidth}{\usebox{\makecvtitlepicturebox}}%
\parbox[b]{\textwidth-\makecvtitlepicturewidth}{%
%\raggedleft%
\ifthenelse{\isundefined{\@insertpersonalinformation}}
{\raggedleft}
{\hspace*{10pt}{\personalinfofont\@insertpersonalinformation}\hfill}% alternate design: \MakeLowercase
{\namefont{\color{color2!50}\@firstname} {\color{color2}\@lastname}}
}
{\color{color2!50}\rule{\textwidth}{.25ex}}%
% optional title
\ifthenelse{\equal{\@title}{}}{}{\\[1.25em]\null\hfill\titlestyle{\@title}}\\[2.5em]% \null is required as there is no box on the line after \\, so glue (and leaders) disappears; this is in contrast to after \par, where the next line starts with an indent box (even after \noindent).
% optional quote
\ifthenelse{\isundefined{\@quote}}%
{}%
{{\null\hfill\begin{minipage}{\quotewidth}\centering\quotestyle{\@quote}\end{minipage}\hfill\null\\[2.5em]}}%
\par}% to avoid weird spacing bug at the first section if no blank line is left after \maketitle
\makeatother
\def\personalinfofont{\normalfont\small}
% end of inserted 1st block http://tex.stackexchange.com/questions/231388/howto-insert-text-beside-of-the-portrait-in-moderncv-casual-style#answers-header
%\title{emty}
\firstname{Max}
\familyname{Mustermann}
\photo[100pt][0.1pt]{example-image}%Portrait-MaxMustermann.jpg} % '64pt' is the height the picture must be resized to, 0.4pt is the thickness of the frame around it (put it to 0pt for no frame) and 'picture' is the name of the picture file; optional, remove the line if not wanted
\usepackage{etoolbox} % http://tex.aspcode.net/view/635399273629833626153770/increase-spacing-in-closing-of-cover-letter-in-moderncv
\patchcmd{\makeletterclosing}{3em}{1em}{}{} % reducing the space betweeen greetings and name in application writing from the original 3em to 1em
\begin{document}
% begin of inserted 2nd block http://tex.stackexchange.com/questions/231388/howto-insert-text-beside-of-the-portrait-in-moderncv-casual-style#answers-header
\insertpersonalinformation{%
\begin{minipage}[b]{2cm}%<- adjust here
\raggedright
\textbf{Geburt:} date, \textnormal{\textit{City}} \\
\textbf{Familienstand:} – \\
\end{minipage}%
}
% end of inserted 2nd block http://tex.stackexchange.com/questions/231388/howto-insert-text-beside-of-the-portrait-in-moderncv-casual-style#answers-header
\address{street}{city}
\phone[mobile]{+49 152 12345}
\email{mm@mail.de}
\AfterPreamble{\hypersetup{
pdfauthor={Max Mustermann},
pdftitle={Lebenslauf | Max Mustermann},
pdfsubject={tabellarischer Lebenslauf}
}}
\maketitle
%\thispagestyle{empty} %https://tex.stackexchange.com/questions/44280/pagestyleempty-doesnt-seem-to-work-for-page-with-maketitle
\vspace*{-8mm} %reduces the space between header and the first CV section
%\pagestyle{empty} % http://tex.stackexchange.com/questions/147849/about-moderncv-footer
\section{Bildungsweg}
%\cventry{year--year}{Abschluss}{Schulname}{Ortname}{\textit{Note}}
[…]
%\closing{Mit freundlichen Grüßen,\\\includegraphics[scale=0.8]{signature.png}}
\cvline{}{}
\cvline{}{Weinstadt, den 01.09.2016 \newline}
\end{document}
erhalte ich mit der aktuellen Version von `moderncv`:
![eine Seite mit Fuß][1]
Der Fuß ist also durchaus vorhanden. Es liegt nache, nahe, dass der Fehler im Code auch die Ursache dafür war, dass der Fuß nicht angezeigt wurde. Wenn man `\makecvfoot` gar nicht aufruft, wird der Fuß eben auch nicht angezeigt.
Fazit: *Fehler nicht ignorieren, sondern ihnen nachgehen und sie beheben!*
[1]: http://texwelt.de/wissen/upfiles/test10_12.png