Many machines made before 2007 have processors that lack features or capabilities required by CloudReady. Especially for users with machines that have Pentium M processors inside, this has proven very frustrating, since those processors should be new enough, but happen to be broken.
In order to keep CloudReady simple and modern, we made the tough decision not to support machines of this kind or older. Most folks will benefit from this choice, but we understand that those with only older machines are missing out.
Here is an alternative for those folks.
Community user ben posted a build from a while back, a Chromium OS Lime build, which supports the "forcepae" parameter which should get Pentium M machines working.
As noted elsewhere, there are other good alternative to CloudReady if your machine won't work - our favorite to recommend is CubLinux which looks and acts much like Chromium OS.