First a bit of background. We run two wireless network in our institution, Eduroam and Guest. Eduroam connects to the university network and allows access to you documents and the servers and connects to the internet on janet, the UK educational network. Guest is used for those occasions when you do not want people on your network. It might be a private company renting a building (therefore not allowed to use eduroam), some visitors holding a conference or some contractors installing CCTV who want to download some updates and drivers, for example. Where Eduroam accesses the internet using janet, Guest uses a Virgin Media service.
I can switch between the two networks on my laptop, I can switch between the two on my android. However, I had a manager come over with his iPad yesterday and said he couldn't connect to Guest. He was getting an invalid password, even though I knew it was correct as I had changed it myself. I tried on my iPhone 3, I couldn't either. Someone tried on their iPhone 4, they couldn't either.
For whatever reason, you have to forget the Eduroam network (and therefore loose all your settings) before you can connect to Guest. Iit is not an invalid password issue because Apple devices that have never connected to Eduroam can connect to Guest.
We have reasons when we need to switch between the two, like when only one of the services is available or if on the rare occasion a service may be full of connected users. This just makes things more difficult.