If you are facing this problem, here is what you should do to fix it.
1. Open your GMail account with the id you used for signing into GTalk.
2. Go to the end of the page (Press "End" button to go quickly). You can find a line like "Last account activity:...."
3. Click the "details" link after that line. An "Account Information" page will open.
4. Click on "Sign out all other sessions".
5. Logout from GMail.
Now open GTalk. Now you should be able to change your status.