|Martin Hawes sends along this tip: (IE6)|
If you add the "ad servers" you see listed in the Back Button drop-down, to the Restricted Zone this will eliminate the Back button issue.
Editors Note: however if you are using Windows XP SP2, you will be prompted by the "Security Center" about a 3rd party connection. Just click No and continue.
Vista/IE7 users should not see any ad servers listed in the drop-down list of the Back Button if your HOSTS file is working properly.