You are using a very old application that isn't supported anymore. There are other apps that you can install and use, plus they offer additional features. It was mentioned that users switched to the Telstra My Connect in order to send SMS messages since the Online Text Buddy is not available anymore, but there is also no website to connect to this service. And if there is, then you have to connect to the member's area on the Telstra website: https://www.my.telstra.com.au/myaccount/home
Secondly, if you have a smartphone, consider installing Viber, WhatsApp, Facebook to send SMS messages or communicate with friends or family.