Exactly the same here. I’ve two Piwik installations:
one from 1.9 to 2.2.2 - no problems
one from 1.9 to 2.4.0 - same as fdtest
After hitting the update key, the web DB update timed out.
So I repeated DB update from bash with the suggested shell command string.
Looks like the entire admin tools are unaccessible.
My language is German (cannot change that, as I’m locked out):
Einstellungen: that’s the one from above
Verwalten: grayed out
Plattform: grayed out
Other subitems seem to work normally.
Found the two files with class definition looking totally different.
Class definition starting with:
2.2.2: 'class ExampleUI extends \Piwik\Plugin’
2.4.0: ‘class Piwik_ExampleUI extends Piwik_Plugin’