Phone certificate not in sin or phone

I am using Nokia 5130. I used to download some good applications but of recent each time i try to download it will alert "no certificate in sim or phone". Pls someone should help me. What should i do to fix this problem

id try doing a factory reset ,all the certificates should be in the phones firmware you can add new ones and delete others but resetting phone should restore the default ones..ages ago i used to get certificate not trusted popups when enter googlemail ,,after googling it i found somewhere that had the new certificate ,i installed that and the annoying certificate not trusted dissapeared ,,,,goodluck google is your friend

Try To download signed apps. Or try factory resetting your phone after backup.

The best tin is flash or update it with pc

Buy htc or galaxy