I am a Kohler Certified Maintenance Technician, and have seen this problem before.
Here is the official solution, as detailed in the manual:
1.6 Internet Configuration and
Security (Firewalls)
When using the OnCue PC application from a remote location behind a firewall, it may be necessary to configure the firewall to open port 808.
The firewall may prompt you to allow OnCue to use port 808. Contact your network administrator for assistance, if necessary.
When the generator set is connected to an intranet network behind a firewall, for example in a commercial or industrial setting, it may be necessary to configure the firewall to open port 5253 to permit an outbound connection.
Contact your network administrator for assistance if necessary.
You can download the full manual for OnCue here: http://ironedison.com/kohler-oncue
The manual is saved on the top right side of the page.