I’ve booted from my USB key and Win PE loads but it then get a “Task Sequencing Error” dialog box pop up that says:

“Failed to find a valid network adapter. For more information, please contact your system administrator or helpdesk operator.”

Contributed By: Cliff Hobbs [MVP ConfigMgr]
This sounds like it’s either a problem with NIC drivers or your machine not being able to connect to the network. Make sure that the “Enable command support (testing only)” checkbox on the “Windows PE” tab of your Boot Image is selected (if you have to enable this then you’ll need to update the Boot Image on your DPs).

Reboot the machine and when WinPE starts press “F8” to start the Command Prompt. Type “ipconfig” in the Command Prompt to make sure you have at least one NIC configured and a valid IP address. In this case there were no valid NIC drivers available as the results of “ipconfig” showed below.

If you are seeing this error on a VMware virtual machine to save you having to modify your boot image to include NIC drivers you can use the following process courtesy of Josh Taylor which I can vouch for:

“If you really don't want to import the VMware NIC drivers in to the boot image you can open you .vmx file and change the ethernet0.virtualDev line to ethernet0.virtualDev = "e1000". The Intel E1000 drivers are included into the stock WinPE image. I did this in my test lab since I had issues with using the adaptive NIC type in my particular environment anyway. There's probably a way to do it in the GUI but I couldn't tell you where it is in Fusion but the vmx entries should be the same across the versions.”

NOTE: This line didn’t exist in my .vmx file so I just added it to the bottom.