Vanhook2 - Thank you very much for your suggestion. It worked.
Most probably, you have not set up your router to assign a specified IP address to the TED Gateway. If you don't do this its IP address will occasionally change, causing the problems you describe. Most routers have an option to specify the IP addresses to be assigned to devices according to their individual MAC addresses (which are fixed and unique). You should use this for any device which, like the TED Gateway, needs to be easily located by software and/or a browser. You should
not, in general, use the peripheral device's setup option to specify its own IP address (if it has this option) rather than defaulting to DHCP, since this can lead to all sorts of problems.