[TYPO3] alt_db_navframe.php not working in be after upgrade from 4.1.5 > 4.2.1

[Raymond Irwin]

Hi List,
I'm really stuck here. I'm not getting any of the Ajax-functions in the 
backend pagetree after upgrade from 4.1.5 to 4.2.1. Even the context 
menus on the icons in the pagetree are gone.

Clean install on the same server works fine, so it's probably not any of 
the php or other server settings.

I tried with and without symlinking the typo3 directories, but no effect.

I dont't know where to look. Any suggestions?

Cheers, Raymond