This evening, our firm began experiencing difficult connecting to Lacerte for initial logins. If users were already logged in, no issues. If they weren't, an error was returned about "internet connection problems".
We traced this back to an App Control rule on our Sonicwall firewalls which categorized the Lacerte traffic from the workstation to Lacerte authentication server(s) as PROXY-ACCESS TOUCH VPN and blocked it. Changing this rule to log, but allow the traffic immediately resolved the issue.
Since we have a change freeze during tax season, it's not clear whether a Sonicwall definition update incorrectly flagged this traffic or something about the Lacerte communication changed and it was re-categorized.
Hope this helps somebody else.