Media sharing in Media player 11

[Barney]

hi,
Have a recent install of vista home premium on which all my videos are stored, this is also connected to my xbox 360 which streams from Media player.

Today I have wasted many hours over a new problem that's just popped up that I cannot solve

has anyone a solution to this problem.

the fault that pops up says:

"Media sharing has been turned off because a required Windows setting or component has changed. For additional assistance, click Web Help."

have followed all the guidance from web help, but no luck.

the only thing i can find is the lack of a folder:
[security ID] subkey
in the registry.

thanks