After upgrading to DS 7.6 HF7 - no longer able to boot client machine(such as Surface Pro) – receiving error "The error read on the device Secure Boot Violation "Invalid signature detected. Check Secure Boot Policy in Setup."
The new PXE files which was changed in HF7, did not got signed by Microsoft.
Workaround - you might disable Secure Boot in computer "BIOS" settings.
Fix will be included in next HotFix and Major version after HF7.
If you require those pxe files at this time, please contact Symantec Tech Support, referencing this Article.