Within last months (never seen it before actually) deployments are not Always successful. You will see the following lines in Status Message Viewer (for a specific system):
-11171: The task sequence manager successfully completed execution of the task sequence.
-10804: The ConfigMgr client was reassigned. The previous site code was "". The new site code is "###". (few minutes later)
-10018: Deployment "########" from site "###" was rejected because the client's platform is not supported. (few minutes later)
At the moment I have contacted Microsoft support for this. They are still investigating the issue, so hope I have more information soon. When anyone recognizes above issue, I kindly like to hear more about it. Maybe it's a bug, but I don't know at the moment..
Some people saying (Microsoft support included) I must change task sequence properties to support all platforms. When looking at the issue this may be the case. Strang thing is I never change this option, so it's on "Run on any platform" as Always. Hope that anyone can tell me how to solve this! Otherwise MS will tell me soon hopefully ;)
Update 8-9-2014: As mentioned by Microsoft and Robert Kloek in comments, a workaround can be used to get the job done. Just deploy the task sequence to "ConfigMgr clients, Media and PXE" instead of using "Media and PXE only". That way a successful message is showed in the end, and not the "Requirements not met" message. This seems to be a change to me, but it helps for sure!