Richard, are you using Windows 8.1 or Internet Explorer 11? If yes, then we have a known issue due to the 'Enhanced Protection Mode'. Please refer to the first FAQ in the troubleshooting guide here and let us know if the problem is not yet resolved: http://go.microsoft.com/fwlink/?LinkID=310093
Senior Program Manager in the Application Insights team.
Right now, load testing is available only in Visual Studio Ultimate 2013 Preview. We haven't finalized the licensing and pricing details for cloud-based load testing. It is free to use at the moment, while it is in preview. We'll publish these details at a later point when it is finalized.
Darshan Desai [MSFT]