First, sorry that this is happening to you! Enhanced SMS & Caller ID uses the Google Licensing server for checking Android license validity. The response you are getting should be temporary.
When you see this message, please make sure that you have a data connection so that the application can check the license. If you have a data connection and you still see the message, sometimes re-booting your phone will clear things up.
If you recently upgraded your phone, make sure that you use the same Gmail account that you used to originally purchase the application, since this account (Gmail address) is tied to your license.
If that doesn't help, please contact me to see if there is something that I can do to help.