Pages error: "The required index.xml file is missing."
I am trying to open a document in Pages 5.2.2 that I have used and opened multiple times before and I'm getting an error message that states "The required index.xml file is missing." There is no option on how to fix this issue and I have no idea what it means. I've been searching to see if there is a later version of Pages that I need to update to but so far I've found nothing. Can anyone help me? I'm a basic user and don't have a lot of technical knowledge but I can follow instructions if someone knows how to fix this. FYI the document was originally created in Word on an old computer but it was literally about 6 years ago an I've been using it in Pages for the last 5-6 years. Thank so much!
Pages-OTHER, Mac OS X (10.7.3)