Many BibTeX bibliography styles -- including, it would appear to be the case, the one you're using -- are set to automatically lowercase all letters in an entry's title field (except if the letter is at the very start of the title field string) if the entry is of type article, techreport, misc, or unpublished. This lower-casing setting, however, generally doesn't apply if the entry is of, say, type book.
Since the title of one of your references starts with ``I don't ... rather than with I don't ..., the I is not the very first character of the title field and hence is converted to lowercase. To keep this from happening, you must surround it by braces, as in
title = "``{I} don't ... ''",
{I Don't}->I Don'tand{I} Don't->I Don'torI don'tdepending on the style. – Marc van Dongen Feb 12 '12 at 14:35