Hi Marcelo,
thanks for the instant suggestion. I unintalled ipython and media box using the application manager and disabled many repositories. Then rebooted as you suggested. I was able to install Canola2 beta6 successfully! Thanks!

Now I will try to reinstall ipython. I think ipython uses dev version of python so that readline is supported. But I have not been able to get readline to work yet. I will have to find the right forum for that question.