Bibtex (natbib): Some Citation undefined

Question

Some Citations in my file are undefined, even tough they are within my .bib-file. I can't find any error.

Here my logfile:

    \documentclass[a4paper,11pt]{article}
\usepackage[left=2.5cm,right=3cm,top=2.5cm,bottom=2.5cm]{geometry}
\usepackage[onehalfspacing]{setspace}

\usepackage[backend=bibtex, style=authoryear-ibid, natbib=true,doi=false,isbn=false,url=false]{biblatex}
\addbibresource{literatur.bib}


\begin{document}


This citation works perfect: \citep{Arthur.}

(Most of my citation work)

This citation does not work: \citep{.Foucault 1980} 


\end{document}

And here is part of my .bib-file:

@book{.Foucault 1980,
 author = {Foucault, Michel},
 year = {1980},
 title = {Power/knowledge: Selected interviews and other writings 1972 - 1977},
 keywords = {Politische Philosophie},
 address = {New York},
 publisher = {{Vintage Books}},
 isbn = {039473954X}
}

@article{Arthur.,
 author = {Arthur, Paige},
 year = {2009},
 title = {How {\textquotedbl}Transition{\textquotedbl} Reshaped Human Rights: A Conceptual History of Transitional Justice},
 pages = {321--367},
 volume = {2009},
 number = {31 (2)},
 journal = {Human Rights Quarterly}
}

I know this one "undefined citation warnings", who states that the user should compile properly:

latex bibtex latex latex

Clearly, this is not my problem, as some of the citations in my .bib-file work, while others don't. I also visited this one: Latex Warning:Citation undefined, who couldn't solve my problem either.

Any suggestions? I really can't see the problem. I have around 80 citations, and from them about 15 just don't work.

Thanks for any help