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
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.