Missing KM Icon after Portal migration

Hi SAP Expert

After we migrate the portal instance onto a different server, we can no longer view any KM Content icon, all the KM Content icons are replaced with a red cross picture instead. The error message I see on the screen is 'The icon is not available'.

We've check, all the KM Content object is still accessible and they have permission 'Everyone-Full Control'.

Does anyone know why we are experiencing this problem? Any suggestion will be most appreciated.