You could try going to the Sony Ericsson website and upgrading your software and see if that works. Just download the programme on the site and it will instruct on what to do (you will need the computer cable that came with your phone). This might not be the solution but worth a try anyway.
If that fails then I am guessing that as your phone is a very recent model, you haven't had it for over a year so it will have a years manufactuers warranty and therefore Sony should replace it for you as it is a fault on the phone
Hope this helps
Shauns
April 2008