The error "No Certificate or does not verify (error 20)" can be caused by a protection software like
Norton, Kaspersky, McAfee, Eset, etc that interferes with synchronization.
Please disable such software and retry to sync.
You may need to disable the firewall or (tune) firewall features that may be called 'smart filtering' or similar.
You should also try the following:
Click RoboForm -> Sync -> Settings -> Proxy Settings (Advanced) and check "Use WinInet layer".