This is indeed a worrying situation – while also the ".idml" file extension confuses me a bit. So I wonder in which file type this document was last saved / which "Element" type you were going to export?
Possible (seldom) workaround to recreate: Create a new document -> menu Document -> Add Pages From File… There choose the corrupted document, sometimes it is possible to import.
Heilix Blechle got a reaction from MikeTO in graphic text isn´t shown in a idml document