There are sometimes incompatibilities between Macs and PC on wireless security -- even down to terminology used.
My own experience is from trying to connect Macs of different generations to regular (PC type) wireless routers.
It's possible that the problem manifests itself when connecting a PC to Apple's Airport (which may be the router they have).
I'd recommend trying to apply the password in HEX format -- but to do that you'll have to get someone with authorisation to access the router's setup screens.