Are you sure? Try running:
reg query HKLM\System\CurrentControlSet\Control /v PortableOperatingSystem
Rahul, hi again. I think you've been somewere abroad because it took you quite a long time to answer.
But anyway, for everyone whom rahul's reply wasn't enough i've got to say i found the solution (based on what rahul wrote but not exactly).
so the most imprtant thing is, that there can be a situation that there is no value "PortableOperatingSystem" (on a path that rahul and your comd promt indicated). then, you should go again to regedit.exe and then (while you are still in regedit.exe) type
the shortcut ctrl+f, or you can find that option also in the upper left corner in "edition" or something like that, next to "file". i found one value containing HKLM\System\CurrentControlSet\Control
/v PortableOperatingSystem and i deleted it. turned the computer off and on again, but it didn't help (still coudn't access app store and so on), so i entered regedit.exe again, and i searched (ctrl+f) for it again. this time value PortableOperatingSystem
looked different, but i deleted it anyway. turned the computer off and on again, and at last i did. now i can create disc image or access app store.
the end of story. i hope it will help someone.
