Error while creating OS X Mavericks bootable USB

Had the same problem. Thought the file "createinstallmedia" was missing, but that wasn't the case. Then I realised I simply needed to make it executable with the following command:

sudo chmod +x /Applications/Install\ OS\ X\ Mavericks.app/Contents/Resources/createinstallmedia

This will create the executable that DiskMaker X initially couldn't find. After running the command above you shouldn't have the error anymore.

Hope that helps :)

Solved it

I copied the same Install OS X Mavericks.app in a different Mac that was running on Mountain Lion 10.8.5 and tried DiskMaker X and it worked. I'm not sure but maybe the reason was that OS X Mavericks GM Build doesn't support the command that was used or maybe there's a different way to copy things on OS X Mavericks using terminal.

Update

I tried making another bootable USB using my Mac (OS X 10.8.5) with the same Install OS X Mavericks.app but failed to do so, it seems that you can only make a bootable USB on the same system that you've downloaded Mavericks on.