I am sorry your receiving an error message. When experiencing text message issues or error messages, we recommend power cycling your phone off and on for 1-2 minutes and updating your phone to the network (PRL update).
To update the PRL:
You may also want to ensure your messaging settings are correct. Setting text and multimedia message options are below:
Press HOME , and then tap > Messages. On the All messages screen, press MENU band then tap Settings to set the text or multimedia message options.
If you continue to have issues, customer service may need to check the system settings for your particular account.