Find My iPhone does not find my MacBook Air
I recently bought this new MBA in San Francisco and brought it to São Paulo (Brazil). I used the Migration Assistant to set it up according to my previous MBP 13", but since then I'm experiencing problems trying to locate the MBA with Find My iPhone. Some times it shows up as "Unknown", although I did name it at System Preferences>Sharing>Computer Name.
I have the same iCloud account set up both on the MBA and iPhone 4S, but sometimes it works, sometimes it doesn't.
Does anyone have a hint on this?
Thanks.
MacBook Air, OS X Mountain Lion (10.8.2)