Client login err_connection_timed_out, why?

Hey folks,

Just starting with WHD. Some starting problems could be luckily solved. But one remains open.

On the machine where WHD is installed we can login via browser, but not from any other machine in the network.

Default link to login is:

https://<ip-adress> :8443/helpdesk/WebObjects/Helpdesk.woa



but BOTH end with err_connection_timed_out

WHD Support referred us to this community for assistance.
Can anyone help please?

Kind regards,