After upgrading System Center Configuration manager 2012 R2 to SP1 (or 2012 SP2), you might see this problem.
When deploying a OSD Task Sequence and not selecting when the deployment will be available (meaning now):
SCCM will auto select Schedule when this deployment will become available and setting the date and time to now (your current time):
But when you for example PXE boot a computer expecting the Task Sequence to be available it might not be so, and in smsts.log you will find the message Skipping Task Sequence because it is not active yet:
Changing the schedule to yesterday or just one hour back will make the Task Sequence available: