Message Sending Failed in Nokia 6600

Hi i want some help about my Nokia 6600. The problem is that i cannot send sms through it. "Message Sending Failed" error is appearing just after 10 sec when i sent message. This is kinda annoying i have checked different numbers now. I read some forums they are saying that edit your message centre no: i dont know that number and i have also emptied my SIM. I have Ufone SIM, its working fine in other mobiles but i am having prob with nokia 6600 only, Thanks

^ Do you have any balance in your account? By the way you can contact your operator for the message centre no.

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Yes i have balance in my account. It usually happens but after tries it works. But now it is not working from two days.

EDIT: OK the problem has been solved by formatting my phone's memory by dialing *#7370#

Such problem occur when your memory is filled. keep your phone memory use to the least.