Since this file is part of Ubisoft's launcher API, an outdated or broken launcher can trigger the error. Uninstall via the Control Panel.
If verification fails, you can manually download and place the DLL. Only download DLLs from trusted sources. We recommend extracting it directly from the Ubisoft Connect installer or a friend's working installation. far cry 3 ubiorbitapi-r2-loader.dll is missing fix