It means that the last time Data Collection ran, the link was not showing up. This could be a transient SNMP problem, the link may have actually gone away, or there could be a bug on the device side or in Campus Manager.
Verify that the link should, in fact, be there. Check to make sure the link is showing as up/up on both devices. Verify CDP is properly reflected on both ends of the link. If all of that checks out, run a new Campus Data Collection.
