Do you have an HII action in your provisioning task?
I have managed to find the problem - The HII Provisioning action when using UNC fails to download all the drivers (including the mass storage driver) I can do it manually and the HII Provisioning action can do it via URL.
Unfortunaly the URL copy is REALLY slow so at the moment I am stuck running it manually.
If you are running 9 SP2, there is a patch that will fix the HII unc copy issue. You have to open a support case and asked for OSD MCP