- did not have any keys (i.e. the network was "unsecured")
- it worked with that setting
- you added WEP key
- now you can't connect
right? If I understood wrong, correct me.
If that's the case, you must just "renew" the connection, so that your network manager doesn't just try to connect with the same settings (no encryption) but connect as if it was the first time. For example if you used the Gnome network manager applet (click on the icon, see the networks available, click on a network to connect) on the panel, you would re-click on the wireless network to disconnect and then again click it to reconnect. You might even have to go as far as picking up the "connect to other networks" entry, typing manually the ESSID in, choosing security (WEP) and trying again. The program might remember the old settings.