For full functionality while using Olark through Google Talk with Google Apps, you are now required to make changes to update your domain's SRV records.
If you are attempting to setup Google Talk and you have a Google Apps account, you will need to first follow the instructions for setting up your site's SRV Records, and then you can follow the instructions for Google Talk. If you linked your Gtalk account prior to setting up your site's SRV Records, then you will need to un-link the account and re-link it.
Use our SRV records wizard to help you with this process.