First of all, please try rebooting both the affected workstation and the server machine.

If the problem persists, please try configuring the firewall on your server to always have port 212 open.

1. Navigate to Control Panel >> System and Security >> Windows Firewall.
2. Select "Advanced settings" and highlight "Inbound Rules" in the left pane.
3. Right click "Inbound Rules" and select "New Rule".
4. Select "Port" and click Next
5. Select TCP and "Specific port" and enter 212 in the text field
6. Select "Allow the connection" in the next window and hit Next.
7. Check all network types and click Next.
8. Name the rule something meaningful (e.g. 212 open) and click Finish.

Note: Versions of Projetex prior to 3D use port 211 instead.