Cannot open a pages document in pages for mac 5.5.3

I created many documents some time ago, apparently prior to upgrading to 5.5.3 (2152) and OSX 10.10.5. When I try to open any of my documents, I get a pop up that says the system cannot open the document. Previously, I could open documents created on my iPad and iPhone with Pages, and vice versa, but not now. How can I sync all these documents again?