One of our users has a personal Macintosh computer that can't access any regular external Web sites when on our corporate network.
In Safari, she gets the message:
Access control configuration prevents your request from being allowed at this time. Please contact your service provider if you feel this is incorrect.
Other browsers produce a similar result.
Ping and DNS resolution work when the computer is connected to the corporate network.
The computer works can access Web sites normally when on a non-corporate network.
All other Macs on the network function corectly. We don't use a proxy server.
Panda antimalware turned off.