In order to start a new session, you need to remove the cookie
ASP.NET_SessionId. If you don't know how to do this, here's the step by step with Firefox:
- While on the "Your session has been locked" page, right click anywhere in the page and select "View Page Info"
- Go to the "Security" tab and click the button "View Cookies"
- You'll see a list with a few elements. Click on the line that has
ASP.NET_SessionIdin the "Cookie Name" column
- Click "Remove Cookie"
Alternatively you can try to restart your browser.