there are other threads here in this forum about this. i think your ZD is running firmware lower than 9.7.
the easiest solution will be to take a old computer, like win xp to connect to the ZD and upgrade at least to version 9.7.2. then you will be able to connect with todays browsers. for that i normally use a win-XP on a virtual PC. may be, you have access to a old laptop.
i think you should be able to upgrade without support plan. at least till 9.7 if you like to keep the settings, just follow the upgrade path. what version is the ZD running now? you also have to check if the AP's are able to run with the newer Firmware.