I have both Pages '09 and Pages 5.5.2 on my iMac. Having problems finding and opening files. Get message: "Can't be opened. The required index.xml file is missing." What to do ??

I have an iMac early 2008, with OS X Yosemite 10.10.2., 5 GB RAM. Having problems with Pages. Have two versions currently on the computer: Pages '09 and Pages 5.5.2. Have been saving documents and at times cannot find them either on Finder or with Spot Light. When I have located them, they cannot be opened. Instead, I get: "Document couldn't be opened. The required index.xml file is missing." I am concerned about losing documents because of this problem.