# pgfkeys error in tcolorbox

I am trying to duplicate part of an example code given in the tcolorbox package documentation on page 13. It looks like this:

\documentclass{article}
\usepackage{tcolorbox}
\tcbuselibrary{skins}
\tcbset{colback=red!5!white,colframe=red!75!black,fonttitle=\bfseries,nobeforeafter,width=(\linewidth-4mm)/2}
\begin{document}
\begin{tcolorbox}[sidebyside,title=Lower not separated,lower separated=false]
This is the upper part.
\tcblower
This is the lower part.
\end{tcolorbox}
\end{document}


It all looks good except for the dashed vertical line that should not be there. The above code generates the error:

pgfkeys:Ido not know the key /tcb/lower separated...


The log file sends me to the pgfkeys package. Section 55 on Key Management (page 481) in the pgfmanual doesn't provide me with an answer.So what's wrong here? Perhaps there's just something missing as in this example: Problem with "Package pgfkeys Error".

And how to give each part a different color?

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Welcome to TeX.SX! Running your example I don't get any errors: do you have the last version? Mine is 2.51 (2013/09/16). –  Claudio Fiandrino Nov 25 '13 at 6:49
I just compiled your example without error messages. My guess is that you work with an old version of tcolorbox. The current version is 2.51 (2013/09/16). The specific key was introduced with version 2.33. You should check your logfile for your version, i.e. a line like Package: tcolorbox 2013/09/16 version 2.51 text color boxes for the current version. –  Thomas F. Sturm Nov 25 '13 at 8:29