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Open diablo III install location (Windows 7: C:/Program Files/Diablo III) Right click .agent.db -> Open with... Select program from list, select Notepad Locate: "supports_multibox" : false, Change to: "supports_multibox" : true, Save file Go to C:/ProgramData/Battle.net Delete the folder titled "Agent"

The biggest problem people are facing when they try to multibox Diablo 3 right now, is the Diablo is running error. Here is a small but sweet solution to this problem. You can just copy/paste and add -launch to the shortcut.You should now be able to open up multiple diablo windows without getting the "Diablo is running" error.