Yesterday I installed CS5.5 trial version, but did not open any files with, CS5.5. Today, when opening *any* InDesign file I get error SharedContent.Indesignplugin missing, more errors, and of course the file won't open. CS5.5 was removed with Adobe's Clean up tool, still unused. Still, can't open InDesign files. It seems CS5.5 embedded itself somewhere.
I don't believe we've seen this reported before. Are yiou saying you never launced CS5.5, and have now removed it, and you are getting these errors?
I would start by trashing the prefs, (see Replace Your Preferences) but I suspect you will need to uninstall everything and reinstall in order.