After a bit of help.
My Kids have been playing Minecraft using their own accounts (not Live) lets call them Player1 and Player2. They have built up a huge and pretty impressive World under Player1 account.
Yesterday we updated them to Silver Live Gamertags accounts (Parental controlled by me), in prep for Player1 to add Friends etc (Gold may be coming later).
But now they are unable to use the Saved Worlds they have been building up, the files etc are there and selectable XBOX just says that a Profile on the XBOX is stopping them from Playing online and will not let them play together Player1 & Player2.
I've Even tried the Adult setting on both profiles and this still does not work.
BUT, if they create a new world under there new Silver Gamertags they can join in each others worlds as and when they like no problem.
This is getting annoying, does anyone have any idea what is going on?