Well, without more details it's hard to give you an answer. Basically the Query Optimzer has decided that, given the available options, a clustered index scan is the fastest access method. It could be that your non-clustered index does not cover the query (include all the columns returned in the select list). If you post some DDL and a query for an example someone may be able to be more specific.
Jack Corbett
Consultant - Straight Path Solutions
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