Citation not shown in pdf [closed]

Question

I have some troubles with citations and biber. I'm citing a paper several times and point to different sections in that paper. But sometimes the citation is not shown in the pdf. I can't comprehend when they are not shown. In one section they are shown properly, and in the other section simply a space appears.

First I use

\cite{Shani2011}

and the second time I use the same (copy and paste)

\cite{Shani2011}

Inside the Bib reference, the paper is also shown properly. I got no errors in my console, just a few Overfull \hbox... and !h float specifier changed to !ht warnings, and one No backend specified, using Biber backend. I don't know why this biber warning occurs, my command to compile in texmaker is (% references the current document name):

"/usr/texbin/pdflatex" -synctex=1 -interaction=nonstopmode %.tex|
"/usr/texbin/biber" %|
"/usr/texbin/pdflatex" -synctex=1 -interaction=nonstopmode %.tex|
"/usr/texbin/pdflatex" -synctex=1 -interaction=nonstopmode %.tex|
open %.pdf

Does anyone know where I can start to debug this?

==========================================

EDIT

Ok, here is a minimum example:

\documentclass[12pt,a4paper]{article}
\usepackage[english,ngerman]{babel}
\usepackage[authordate]{biblatex-chicago} 

\bibliography{Bibliography2}

\begin{document}
    \cite{Shani2011} blabla. \cite{Shani2011} blabla
\end{document}

This produces

Shani und Gunawardana 2011 blabla.  blabla

The second citation doesn't gets printed into the pdf. But I found out, if I cite between the two Shani2011 another paper, it works. This

\begin{document}
    \cite{Shani2011} blabla. \cite{Shani2009} blabla \cite{Shani2011} blabla
\end{document} 

produces this

Shani und Gunawardana 2011 blabla. Shani 2009 blabla Shani und Gun- awardana 2011 blabla

So I don't know why this doesn't work. Any ideas?

EDIT

Here is the Bibliography2.bib:

@article{Shani2011,
author = {Shani, Guy and Gunawardana, Asela},
title = {{Evaluating recommendation systems}},
year = {2011}
}

@article{Shani2009,
author = {Shani},
title = {{Evaluating recommendation systems}},
year = {2011}
}

EDIT

Here is the content of the Masterthsis.blg:

[1] Config.pm:361> INFO - This is Biber 1.5
[302] Config.pm:364> INFO - Logfile is 'Masterthesis.blg'
[1209] biber-darwin:193> INFO - === Tue Mar  5, 2013, 10:19:55
[1210] Biber.pm:327> INFO - Reading 'Masterthesis.bcf'
[1426] Biber.pm:619> INFO - Found 1 citekeys in bib section 0
[1841] Biber.pm:2976> INFO - Processing section 0
[2305] Biber.pm:3086> INFO - Looking for bibtex format file 'Bibliography2.bib' for section 0
[2449] bibtex.pm:764> INFO - Found BibTeX data source 'Bibliography2.bib'
[4823] Biber.pm:2860> INFO - Overriding locale 'en_US.UTF-8' default tailoring 'level = 4' with 'level = 2'
[4823] Biber.pm:2860> INFO - Overriding locale 'en_US.UTF-8' default tailoring 'variable = shifted' with 'variable = non-ignorable'
[4823] Biber.pm:2866> INFO - Sorting 'entry' list 'nyt' keys
[4824] Biber.pm:2870> INFO - No sort tailoring available for locale 'en_US.UTF-8'
[5115] bbl.pm:462> INFO - Writing 'Masterthesis.bbl' with encoding 'ascii'
[5116] bbl.pm:535> INFO - Output to Masterthesis.bbl

Answer 1

I figured it out, 'cause @PLK pointed me to the right direction. It seems that an outdated biblatex-chicago package caused the problem. I thought I updated everything to the latest versions, but my package manager on OS X, Tex Live Utility, just updates partial. So I had to re-run the update process a several times (and Tex Live found after every update new versions), now it's fixed. May this helps somebody else.