Firstly Barry, i found out ( it took some time too ) that the S75 Cybershot cannot use any Memory Stick Pro or Pro Duos in an adapter.
So the upshot is that only the original 8-128mb sticks can be used
As for the problem with the original stick, i dont know why, ...but what fixed it was pressing the tiny reset button on the bottom, which is so small i needed the manual to tell me where it was. This needs a fork prong or a ball point pen or something.
Soon as this was pressed, the card started working.
I found some info the net , again this took a while, that formatting these cards on the PC should be done using FAT if under 4gb, and FAT32 for 4gb and over. I dont know if that was the problem