GlobalProtect uses the built-in Microsoft Internet Explorer libraries to create the login popup for CalNet authentication. If the security settings on IE have been changed from the default "Medium" or JavaScript has been disabled the login pop-up will not work correctly.
If the system needs to have customized security settings for IE users should set vpn.berkeley.edu and *.vpn.berkeley.edu as trusted sites and that the security level for trusted sites is set to Medium.