Duplicate slugs in wp Database

While updating a category I keep getting "Item not updated" message, after a little research I found that it is due to duplicate slugs in the database.

I know a slug cannot be duplicated, so now I am wondering how is this possible that database has duplicate entries for slug and how can I get rid of these?

I am using WP-ecommerce categories, where these errors keep coming.

You can see the duplicate entries in term_id 27 & 963.