Mavericks update: This disk cannot be used to startup your computer

I tried to update from my current 10.8.5 to 10.9 but was unable to. I downloaded the "Install OS X Mavericks" from the AppStore. Once I ran it, I got the following error message: "This disk cannot be used to startup your computer". Here is a screenshot:

Of course, I beg to differ, as this is the disk I am currently booted on. I searched a bit on the internet. I found the following support article:

http://support.apple.com/kb/TS3926

It is originally for the installation OS X Lion, but the problem seems similar and it was suggested to try it in some other thread. The suggestion is to resize the intended install partition to make the size slightly smaller However this was not possible as, in the Disk Utility interface, there is no way to resize any partition. Here is a screenshot:

Here is the info panel for the Epiblast partition:

Any ideas ? Help greatly appreciated.