Reasons unable to access Gigaset Web interface:

In order to connect to the Gigaset web interface for the Gigaset phones you need to make sure that your PC or Mac computer is connected to the same router that the VoIP broadband phone line is connected to.  

So that when you enter in the VoIP IP address it will pick it up from the right broadband line (the one connected to the VoIP phone lines).

Please also check which browser you are using to access the Gigaset web interface from - some people have reported issues when trying to access from Firefox browser but can successfully login via Google Chrome browser.

Also check you have correctly entered your VoIP IP address - please try missing out the last 0 out of the address as sometimes this can make a difference to accessing the web interface.

Please Note: 

Some businesses run 2 broadband lines one for the the team using the internet for their software etc and another separate broadband line for the VoIP phone lines.  

If you are trying to log into the broadband (IP address) not connected to your VoIP line then an error will occur and it will not connect you to the Gigaset web interface when you type in the VoIP IP address into the browser window as you have connected to the wrong network.

Just check the cables from the PC or Mac to see which broadband line they connect up to on the router box.  You may need to log in via another PC (that is connected to the VoIP phone lines) to access the Gigaset web interface.

You may find, that you need to plug an ethernet cable directly from your PC or Mac into the LAN port on your router to pick up the broadband line that runs your VoIP phones.  

Where you have desk phones plugged into an ethernet hub box ensure that the hub box is plugged into the router that runs your VoIP lines, then ensure that your PC or Mac is then plugged directly into that router so that it can pick up your VoIP IP address address.  

Please see example of an ethernet hub box below:

Once you have made sure of the above you can then enter your VoIP IP address into a web browser on that computer and you will then have access to your Gigaset web interface.