Cause: You downloaded the offline update for ESET NOD32 version 10, but your offline PC has version 14. Solution: Always match the offline update file to the exact major version installed. You cannot use a v10 update file on v14. Check "Help" → "About" to see your version first.
If you cannot configure a mirror, you can use a standalone offline update file (often ending in .nup or .exe). This is essentially a snapshot of the virus definitions at a specific moment. eset nod32 offline update top
This is the simplest method. ESET provides a downloadable file named update.7z (or similar naming conventions depending on the version) on their official support page. This archive contains the latest virus signature database. Cause: You downloaded the offline update for ESET