error message connecting to network

Does anyonw know what "there was an error connecting to the network. Try 
again" means please?  I am getting this error message whenever connecting
my 
Macbook, Ibook (air****t extreme card) and PowerBook (air****t card) to my
WEP 
protected network.  I am also getting it when connecting to a neighbour's 
open network.  I don't get it all the time however. I only get it on
certain 
open networks and as I say, always on my WEP protecte network.

Needless to say, no 'Try Again' ever gives any different result.  pressing

the down arrow to scan for networks and trying to connect that way when
one 
of these networks is shown throws up exactly the same error message.

I have about a half dozen computers here and none of the non-Mac ones give

any such error message.  They all just connect or dont (if the signal is
too 
weak).

I have shown this to the Apple Genius bar.  They got it when they tried to

connect to their own Apple Store open network and (now) two or three of 
their geniuses have told me that they have never seen this error message 
before and they dont know what it means.

Googling it just throws up the obvious answers that I am entering the 
password incorrectly which obviously isn't the case here.