Quick question -- how is this network secured? What's serving the network (Airport stations, non-Apple, etc.)? Is there a user/password that's saved, or is there some other client verification?
Just wondering. I feel your pain, though. Some of this is voodoo, including incompatibilities with some wireless hardware and OS X / Airport. I'm on a network right now (granted, a home network, not industrial-strength) with a Linksys router that occasionally won't grant a connection to this laptop after it wakes from sleep. I've been troubleshooting it for months, but usually just give up and restart the router, which "solves" the problem.