I initally wanted to do a "clean" install of tableau 8 SERVER ( instead of an upgrade). I uninstalled tableau 7.0.1, rebooted the server and then installed tableau 8. When I tried to access the server I then got an authentication error and could not log into 8.
** If you have a previous version of tableau installed on your server* be sure to manually delete the tableau directory after uninstalling earlier versions. Then install tableau 8
For Tableau 8/WIN2008 R2server, you need to specifically delete the following:
C:\Program Files (x86)\Tableau