after reading this discussion @ forums:
I tried here the import feature... and after picking some activities an press the "execute" button, I'm getting:
Notice: Undefined variable: results in /backup/import.php on line 103
Fatal error: Call to a member function delete() on a non-object in /backup/import.php on line 103
Appart from this, the guy in the discussion is also reporting one "cannot_finish_ui_if_not_setting_ui" exception. Not really sure why this gets thrown.
If you can request more information (debug enabled...) and take a look to this... it will be great, thanks!