Your client was struggling to find nearby peers and all we did was specify certain reliable nodes to connect to.
The problem is discussed at length on this thread: http://forum.bitcoin.org/index.php?topic=9821.0
This should be fixed in the next release which is due very soon.
If you check "Map port using UPnP" box, in all likelihood you won't have to do this again.
My guess would be that In System preferences->Security->Firewall tab changing your settings is locked. If you press on the lock icon in the left bottom corner and enter your password you should then be able to go into your bitcoin preferences and check "Map port using UPnP"