I kept getting “A required device isn’t connected or can’t be accessed” in MDT/WDS.
I had no idea it was actually a cumulative (March) windows update that broke the WDS server this week.
The MS article says “After installing this update, there may be issues using the Preboot Execution Environment (PXE) to start a device from a Windows Deployment Services (WDS) server configured to use Variable Window Extension. This may cause the connection to the WDS server to terminate prematurely while downloading the image. This issue does not affect clients or devices that are not using Variable Window Extension.”
- Disable TFTP Variable Window Extension inside WDS properties.
Here is the MS article regarding the issue.
MS are working on a patch soon.
UPDATE 10/07/2019: It appears the June CU KB4503276 for Server 2012 R2, which was meant to fix the PXE booting issue is causing a PXE boot issue in WDS / SCCM
Uninstalling the update will fix the issue for now.
If you are using SCCM you can turn on the native SCCM PXE server: Go to Administration > Distribution Points > Open the properties of your DP > PXE Tab > Tick “Enable a PXE responder without Windows Deployment Services”. This will take a few minutes and no reboot is required.