I logged a PSS call a while ago (as im sure many others did) regarding bootsect.exe in config Manager 2012 R2 not being recognised as a valid win32 application on XP machines….. this caused errors when using 2012 R2 and the boot.wim needed to stage on an XP machine – a common scenario for a refresh build.
the work-around was to grab the bootsect.exe from ADK 8.0 – but, now the hotfix for this is publically available.