exclamation mark on airport icon... internet sharing not working!
i own a macbook pro 15' late 2008 with leopard (10.5.8); my sister owns a macbook pro 13' late 2009 with snow leopard (10.6.2).
we used to connect one of our mac to the internet with a internet key and connect the other one to the first using internet sharing via airport.
it is about a week that internet sharing gives problems (neither I nor my sister have not changed the settings): the mac with the internet key works just fine, you can use internet and activate internet sharing; when you try to connect the other mac to the first by airport, it keeps the connection for about 5-10 seconds, then an exclamative mark appears on the airport icon and if you click on it there is a warning saying "no internet connection" as you can see below:
http://img203.imageshack.us/img203/5044/immagine5k.jpg
("macbook pro" is the network i created with my mac; i took the screenshot on my sister's mac after trying to connect it)
when this happened for the first time, i looked in System preferences > Network; clicking on "Airport" i could see "Airport has an autoassigned ip and may not be able to connect to the internet" (this appeared on both mac when they where connected)
when i saw it i went on "Advanced" and i set manually the ips (192.168.1.1 for my mac, 192.168.1.2 for my sister's)
after this the writing changed to "Airport is connected to macbook pro with the IP address 192.168.1.X" (the X was 1 for my mac, 2 for my sisters)
i tried almost everything, i deleted some .plist files in library/preferences/systemconfiguration as written in some thread on apple forum; i deleted the airport system preferences and re-introduced them correctly, i tried the same on my sister's mac but it still don't work.
the key can't be the problem because it always worked and it still work for the mac directly connected. i read in internet that the "exclamation mark problem" is quite common for snow leopard user and many of the thread on apple forum were recent (january-february-march 2010).
may the problem depend on some updates? i tried to update my and my sister's mac after the problem came up but it still don't work.
please, help me...!!
MacBook Pro 15' late 2008, Mac OS X (10.5.8)