Usually, the “attempting to authenticate to a non-existent session” error occurs because your browser does not accept cookies. Please change your browser settings to accept cookies
Instructions for the most common browsers: http://academicguides.waldenu.edu/sst/technology/browsers/enable-cookies
After you have changed your browser settings, clear your cache.
If you are using Internet Explorer, make sure that your privacy slider is set to “Accept All Cookies”, the lowest setting.
Click on the "Tools" menu and Select "Internet Options". Note: The "Tools" menu looks like a gear in Internet Explorer 8 and 9.
Click on the "Privacy" tab.
Move the slider to "Accept All Cookies", the last option.
You may also want to use an alternate browser, such as Firefox.