I have a solution!!!
Extract the mission files from the campaign PBO and open the mission in the editor.
Then when the mission is loaded, click op 'preview' or something, so you'll play the mission via the editor.
There it will get past the stuck dialogue. Now save and exit.
Then go to the savegame folder and copy the savegame from the single mission, to your campaign save folder et voila it works!!
(don't forget to backup savegame)