"The document is invalid. The index.xml file is missing".
I suddenly can't open any of my Numbers docs. I get a msg "The document "name of doc" is invalid. The index.xml file is missing". I literally had the document open this morning with no problem, closed it, tried to reopen it and now I get this msg...all in the same computer session. It didn't start after an update or anything, just in the middle of a computer session. Seems to affect all Numbers docs. I can't open any of them now. I'm running OS X El Capitan Version 10.11 and Numbers 09, Version 2.1.