Duplicate references can cause a number of issues in the creation of a bibliography. If both instances are cited in your paper, they will show up twice in the bibliography, even though they are the same citation. If you delete a duplicate reference and it has been cited in your paper, you will receive the error message "Reference 2317 was not found in your database" when trying to format your paper.
To get rid of duplicates, access your duplicates list from the "View" menu. "Exact Duplicates" have the same title, author, and publication date, while "Close Duplicates" are looser matches that RefWorks has flagged for possible repetition.
RefWorks will display all duplicates, with one instance already checked. Delete these copies by selecting the red X. You should delete the reference with the higher ID number, as you're less likely to have started working with it in a paper.