Dhass are you on a BIS or BES. My assumption is that you are on a BES. If you are, resending service books or upgrading/downgrading your OS will most likely not work for you. I JUST had this issue with a user no more than 20 minutes ago. I used the search button in this forum and found the answer in seconds
. You will need to remove the user from the BES and re-add them and then activate the device again. You do not have to wipe the device. If you do, and back the device up, when you restore it, you will have the same problem, so a restore is out of the question.