If you’ve installed any recent build of Windows 7 Beta using an internal utility to mount ISO files as virtual drive; you would definitely encounter an error, if you launch your Zune software i.e. none of the DRM-protected songs from the Zune Marketplace would play.  Each DRM-protected song would display a small yellow exclamation mark next to it.  When I clicked on the exclamation mark to see what the error message was, this is what was displayed (screenshot).

Cause: The utility to mount ISO files make changes to the Boot Configuration Data.

Resolution: Just run MSCONFIG.EXE (or BCDEDIT.EXE from an elevated command prompt, or run BCDEDIT /DEBUG OFF command), check for the debug switch, it’ll be on, just uncheck the option and reboot your system, and voila! everythingback to normal again.

Additional Resources:

• MSDN: Kernel-Mode Code Signing Policy (Windows Vista and Later)
• MSDN: Plug and Play (PnP) device installation signing requirements
• MSDN: BCD Boot Options Reference
• MSDN: BCDEDIT /debug
• MSDN: TESTSIGNING Boot Configuration Option

Source:→ TechNet Blog