We are testing an upgrade from DNN v6.02.09 to v8.01

Upgrade was successful, however now we have a problem where we cannot enter the EDIT mode of any page. When we click the "EDIT THIS PAGE" button, it pops up a small white (blank) dialog box with a spinning circle for a few seconds, then the site redirects to the homepage in regular VIEW mode.

I checked the Event Log, no information is posted there. So I can't tell what is causing the problem since no error is logged.

Anyone encounter this problem and/or know of a fix?

Help!