The server you are trying to reach is offline, or your network blocks WebSockets (common on school Wi-Fi). Solution:
In the vast and ever-expanding universe of Minecraft, few things are as cherished as the game’s history. For many players, the "Golden Age" of Minecraft is forever tied to the 1.5.2 update—colloquially known as the "Redstone Update." It was a time of simplified mechanics, classic PvP combat, and a raw survival experience that many feel has been lost amidst the modern updates and microtransactions. File Name- Eaglercraft-Launcher-1.5.2.zip