Nokia 5230my texts will not send?

[Kerry E]

i have the Nokia 5230 On network orange , my phone used to be fine up untill now , it just randomly happend i have great signal and credit but my texts will not sendNokia 5230 texts will not sen , i can recieve them and ring people ect but not send texts it says message sending failed, its not my simcard as i put my simcard in an old phone and it is fine the messages send, its not the message center number or anything as i have checked that. does anybody know how to help me please ? would be much appreciated