connecting Macs to a wireless network

[#1]

My son's home from uni (yippee  :-\)  He has his Mac Book Pro, and can connect ok to my network, but when he's at his girlfriends, it won't connect to her dad's network. (We both use the same model Belkin router by coincidence)
He knows the WPA passkey, but it doesn't like it (I asked him to check the usual - upper or lower case etc)
If they turn off the security, then it'll connect, but obviously they don't want to do that.
Any suggestions? 
John

[#2]

Are both routers set to the same flavour of WPA ?
There are lots of different variants ( see here http://www.darknet.org.uk/2008/12/confused-by-wep-wpa-tkip-aes-other-wireless-security-acronyms/ )
Maybe one is set to WPA2 or maybe AES instead of TKIP ?
Hope that helps

[#3]

He says WPA with passkey (I'm pretty sure that the router won't handle WPA2) and it works ok on my router, so I don't think he's using the wrong one on the Mac, but I'll check to be sure.
Thanks
John

[#4]

Normally gives some kind of error if it won't connect, is it saying anything?
Other thing is does the other router have MAC filtering on?

[#5]

MAC filtering was off (he checked) and I think the error message was something like password incorrect.
John

[#6]

Not got a hidden SSID?

[#7]

The SSID was visible, and the Mac tried to connect, but the message just said that the password wasn't accepted.

[#8]

Have they tried changing the password?
I know it sounds silly...

[#9]

I run a mac on a network and the router is WPA2 so that maybe the problem

[#10]

What version of OS X is the Macbook Pro running? Early versions of Leopard (10.5) had issues with connecting via Airport to certain wireless networks, but Apple seems to have fixed this since 10.5.3 or later. The latest version is currently 10.5.6, if running Leopard, I'd suggest downloading and installing the 10.5.6 Combo Updater - see here - the Combo version can fix things that the incremental updates occasionally break (or miss). If it's running Tiger (10.4) then this probably won't not be relevant.
Sometimes you need to insert a $ before the password on a Mac with certain routers. It could be worth trying that.
Finally, check the router's firmware is up-to-date.

[#11]

Having the same issues now.  Woke up one morning and the router has decided to bump the macbook off. No error message, but it just doesn't connect to the Voyager 2110.  iPhone comes up with a different error saying the password has been rejected.  Know its correct, tried changing a few times, upgrading hardware etc.
Running Snow Leopard

[#12]

It might be a stupid question, but have you tried rebooting the router?

[#13]

As in a normal on/off or a reboot via the config manager?

[#14]

Tried a reboot via the config manager.  Seems like I can connect....
As I typed that I got a lost connection symbol on my airport, can only get a connection via the ethernet cable.  iPhone seems to hold the connection until I go upstairs and it drops.  Used to be able to get a connection in the upstairs bedroom no probs.  No changes in the modems position, electrical items around it or anything.  Very frustrating.  Last time a firmware upgrade solved this problem.  Router is fully up to date.

[#15]

Right, iPhone seems to work (Not checked range yet) Macbook can't connect.  Whenever I go into network diagnostics its telling me its connecting to the modem but cannot get the network settings.  Can take a screenshot it needs be.  The security is correct, so is the password.  No idea what to do next.