My wife had a spreadsheet with lots of references and complexity that she was working with for hours.  She saved the file in Excel 2007 and something went wrong – she was unable to open or use the file in Excel 2007.  She downloaded the original and spent hours working on a second copy.  I arrived home to find she was completely frustrated because the same thing happened a second time.  We discussed a couple options to try and fix the problem (she had already sent the spreadsheet to someone else to see if it was just her computer/setup/etc.) – finally we opened the file on Windows 8 with Excel 2013:

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Excel 2013 not only fixed the issue, it documented the problem (<repairedRecord>Repaired Records: AutoFilter from /xl/worksheets/sheet2.xml part</repairedRecord>) and the saved file worked in Excel 2007 just fine.  An enjoyable evening was had by all after solving this problem (I just wish I had arrived before the 2nd round of time filling everything out!)