Dunno exactly - I don't do Windows.
But I'd try two things. Look for the file in that directory, and right-click 'open with LibreOffice', or 'Open with Other Application....' (or whatever the Windows equivalent is). And/or, from LibreOffice, select 'Open' and navigate to that file in that directory.
Maybe the association is looking at an older installation of LibreOffice? I'd try deleting that association and resetting it with the current location of LibreOffice (again, not doing Windows, that might need a little translation, but something along those lines). Or google for this condition, maybe the EVIL Microsoft likes to interfere with anything trying to take MS Office's place?
-ERD50