Can't open Indesign file. Error message says I need to upgrade plug-ins?

I created a business card for my husband from my indesign 5.5 version. I haven't upgraded my version since creating the file and for some reason I can't open the file. I get the error message 'Cannot open "Business Card - Ryan.indd". Please upgrade your plug-ins to their latest versions, or upgrade to the latest version of Adobe InDesign.'
When I look at the business card file with finder it says it was created with InDesign 5.5. When I view my InDesign application through my finder applications it says I have InDesign 5.5 so I'm not sure why this error message is saying to upgrade my version of InDesign.
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I wish I had a dollar for every person who claimed there was no way a file was saved in a later version only to find out it was.
If you post a link to it someone here will save it back for you.