Problem with 4 GB M2 Card in w910

Friends i hav a new question.Have anyone of u tried using 8gb m2 in ur w910i?I am now using a 4 gb card in my w910i.
Do reply soon,hav got good offers from e-bay india
THANKS

guys,
i tried all the options stated above already.
i doubt there is a problem with the card firmware because sometimes when using it with the PC, I'm getting Access denied/write protected error when pasting files into card. I mailed Sony for this, but no replies:(

You HAVE to format the card in your PHONE (File Manager) otherwise the card won't work in your phone.

Do that and your problem gets solved.