I have been trying to upgrade a site from EE 2.5.5 to EE 2.8.1, but I get a white screen on the admin.php page after the upgrade is complete. The only way to get rid of the white screen is to disable extensions in the config.php file. I also get the login window that usually appears after the usual non-use timeout, except it is not a popup. This happens, when I am logged in. It appears at the bottom of the control panel - see screebshot below.
I have tried upgrading all plugins, but so far I cannot enable extensions without getting the white screen.
I have upgraded numerous sites to EE 2.8.1 but none have been this problematic. Any sage advice is welcome.