This started to appear in my Vista x64 event log after changing the CPU. Side effects visible elsewhere included inability of Windows Movie Maker to split Media Center recordings and crash of Windows Media Player 11 when playing Media Center recordings.
Error 0xC00D278F refers to NS_E_DRM_HARDWAREID_MISMATCH, which is described at “Windows Media Format 11 SDK Error Codes”. Judging from the description, this error would mean that any hardware change could provoke it. Even as innocent as CPU change or upgrade of graphics card (Google found at least one report of upgrade from NVIDIA 6800 to 8600 causing exactly the same symptoms). The solution is available in
ME891664. In short, all files have to be removed from the folder "%SYSTEMDRIVE%\ProgramData\Microsoft\Windows\DRM". After that, you can re-individualize DRM system by going to “Security component upgrade“, and clicking on upgrade button.
This would mean that DRM licenses must be backed-up before any hardware change on Windows Vista systems. After any upgrade of hardware, the link “Security component upgrade” should be checked as well, as a JavaScript error on the page means that DRM data files have become invalid and have to be deleted. Because I do not have any Windows DRM licenses, I did not try to find how to back them up in Vista, but Windows Media Player menus referenced in KB did not exist at this time.
Unfortunately, there is no simple and visible warning for less experienced users that their DRM files became unsynchronized with their hardware.