MacBook won't detect Closed Network automatically

My MacBook (OSX 10.5.8) won't automatically detect the closed network at work. It'll work fine if I choose "Join Other Network" and type in the Network name and the WEP Password. It will also not automatically remember the password. I have to go into System Preferences-Network-Advanced, and copy the password from the Preferred Networks. At home it works fine, and it auto-joins my wireless network (which is not closed). Because the Closed Network is at my work site, I don't have authorized access to the base station. Other colleagues with the same laptop do not have this problem, and my old macbook (OSX 10.4.10) works fine.