Our engineers are still looking into the issue at this time. Google Calendar sync does, however, work in PersonalBrain 6. If you already purchased and registered PersonalBrain 6, you can simply open your brain in PB6 and use Google Calendar sync from there. Everything that is synced in PersonalBrain 6 will carry over to TheBrain 7 beta if you choose to go back, but you will have to always sync in v6 until we are able to resolve the issue in v7 beta.
TheBrain 7 is backwards compatible, however once you open a Brain in version 7, some features will be incompatible with earlier versions. Be sure to make a backup copy of your Brain prior to opening it with version 7. If you would like to roll back to version 6, you will lose any link notes and/or link attachments that were created in version 7. Also, after you reinstall version 6, you will need to rebuild your instant activation index by clicking on the File menu, click Utilities and select Refresh Instant Activation Index.