Macbook Pro can't find properly working Airport Express network

Question

I have an Airport Express that's set up and working properly, and my Mac Mini and my iPhone both find the airport network, but not my MacBook Pro. The MacBook pro is even closer to the Express than the Mini is, and it finds many available airport networks (from the neighbors), but not my own network that the other units find without a problem - my own network just isn't listed among the others on the MacBook Pro, and Airport Utility on the MBP can't find the Express either. I've obviously tried restarting everything, as well as resetting the Express and setting it up again (which works just fine from the other two units), and I've tried creating a new user account on the MBP and check from there, but no go. The MBP runs the latest version of Snow Leopard and works just fine with other Airport Networks (at work, or one of the neighbors networks even), so it shouldn't be faulty hardware. At some point it's time for a Lion update for the MBP and then we'll see if it's some weird system software error that gets resolved in the process. But until that happens … what else could I try?
I'm thinking maybe this is some 802.11 b/g/n malfunction? The Express is an old g, the iPhone is g only, and the Mini is an old g as well, but the MacBook Pro is newer and supports n … but it should of course still be able to switch down to g and find the **** network (or the Express when running Airport Utility).
Anyone?

Answer 1

Well, I can't delete the wireless connection since it doesn't really exist (on the MacBook Pro). Had the Express in my office, but brought it home, and reset it there and created a new network using the Mac Mini, so the MacBook Pro had never been connected to that newly created airport network. But I did delete a lot of old saved connections, some of which were from when the Express was used in my office. This was however, before I read your reply here, so I didn't also erase the passwords from the keychain, however. But still no go; the MacBook just wouldn't list the new network among the available ones, or list the Express in the Airport Utility.
But then … last night, for no apparent reason whatsoever, suddenly everything just works.
In trying to wrap my head around this, and learning from it. Is it even possible for an old network used on an Airport device to interfere with a new network created by the same device? What I mean is, does the computer identify the airport by some sort of serial number or something, regardless of the network created by the airport? So that when a computer should be looking for a new and current network on an airport device it instead looks for an old network it has previously been connected to on that same airport device? Assuming the old network should still exist on that same device, and therefore skipping to look for a new network on the same device? I mean that would suck, but if that's the case then at least I'd know to always erase all traces of any old connections for a specific device in a case like this. ;-)
Thanks for your input!
Cheers!