Diablo 2 1.10is required to play on the Ender realm. If you need to revert back to 1.10 use this to revert to 1.09 then install the official 1.10 blizzard patch

Download Gateway Editor located here.
Select the Diablo2/Diablo2Exp tab at the bottom.
Click add gateway and add the following infomation;

Name: Ender
Zone: -5
IP: bnet.tog.net

Click OK and close Gateway Editor.

NOTE:
You can also use the Ender registry quick server add to do this automatically (may remove other private realms in your list) - just double click, press yes to add to registry and it's done.