last time I took a look at the Unknown computer object created when a task sequence fail http://larslohmann.blogspot.com/2013/11/unknown-computers-and-required-task.html.
But in some situations this object is not created, let try to remove the network while WINPE is downloading:
It will off course fail and if you try to PXE boot again we are back to No boot filename received :
Again the PXE log will show:
no advertisements found
No boot action.
Rejected.Not serviced.
This time we are unable to use Clear Required PXE Deployment because the computer is simply not shown in the GUI.
If we take a closer look at the table LastPXEAdvertisment, we will find the MAC address in the table.
So how are we going to be able to PXE boot this computer again?
One way could be to import a computer into SCCM with the MAC address, Clear the PXE of this machine and delete the computer again, this way it will be back to unknown without any previous PXE boot.
Another way is to delete the entry in the table 
Maybe there is something that I have overlooked, but should this really be a problem?
Please let me know if some of you got a better solution.
