So I updated to the latest version using the App Store as I was getting the same error as described on the 1st page of the support pages.
After doing this I restarted my mac and applied the license key using the "retrieve my key" from the support page.
I then restarted my mac again - I am able to login to 1password and sync my value with dropbox - however the 1password mini says "read only - click here to buy". Obviously I am not going to buy a license again - but clearly something is out of whack...
1Password Version: 6.6
Extension Version: Not Provided
OS Version: 10.12.4
Sync Type: Dropbox