If your site uses a remote SQL Server for VisitorRego’s database, Windows Firewall may block the connection between the VisitorRego unit and the SQL Server.
Port 1433 (TCP) may need be allowed for both inbound and outbound traffic to ensure VisitorRego can establish and maintain the connection.
Video Tutorial
A quick walkthrough of how to allow SQL port 1433 through Windows Firewall:
How to Allow Port 1433 (Inbound & Outbound)