Actually, a minimal working example is one in which you remove all code not related to your problem -- and especially things like images that make the code uncompiliable for those who don't have them. I had to comment most of that out to compile your source.
I don't think the problem has to do with including the title page from a separate file. I get a problem even if I copy and paste the code inside.
Two things worked to fix it for me in TeXworks.
The first is to switch to UTF8 encoding and option for the inputenc package. This presupposes your editor can save in that format.
Code: Select all
\documentclass{article}
\usepackage[ngerman]{babel}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\begin{document}
äüö
\end{document}
The other is to switch to the LaTeX accent codes to make the umlauts.
Code: Select all
\documentclass{article}
\usepackage[ngerman]{babel}
\usepackage[latin1]{inputenc}
\usepackage[T1]{fontenc}
\begin{document}
\"a\"u\"o
\end{document}
That doesn't really explain what the problem was though, since latin1 should be able to handle the umlauts... but I don't have a lot of experience with it, since I pretty much always use utf8.