I have a rooted Samsung Galaxy S2 with GB Samsung firmware, I have updated Viber through Google Play and now it won't even start. It gives me a crash error dialog and closes without even starting the UI. I've read the solution for this issue is to reinstall Viber, but it would also mean that all my chat history will be deleted, and I want to that. How do I backup and restore ONLY the chat in Viber?
As your phone is rooted, you could use Titanium Backup to backup app and data. Then uninstall Viber, re-install it, check if it works, and use TB again to restore only the data.
Keep in mind that when a mis-configuration is the cause of your problem, after restoring the app's data your problem might be back. In that case, simply repeat the operation, but do not restore the data, if you want the app working again. Of course, in that case your chat history would be lost; but you might be able to manually pick the data from TiBu's backups.