Having duplicating content will affect your search engine ranking in some way, and is definitely not recommended. You should be keeping your content unique and of quality.
However, if you really have no choice, you can set a rel="canonical" tag in one of the duplicated pages, to let search engines know which is the preferred version amongst your duplicate content. This FAQ from Google Webmaster should help you: [support.google.com...]
If I were you, I would try my best to remove duplicate content, since the canoncial tag is not yet a perfect solution.