This message does not actually mean you have duplicate fields. It means that a child class has inherited this field AND has a separate dictionary entry for it. That is to be expected in all CMDB tables. But not necessarily always the case in asset tables or other tables. There was a point in time (maybe Fuji or Geneva?) when this happened; prior to that, field inheritance was implicit everywhere and did not result in cloned dictionary entries. Bottom line is that it is fine to have an inherited field defined with a separate dictionary entry and this is exactly what you would expect to see if that is the case.
That said, it begs the question whether it was the alert message that caused you to think that you have a duplicate field? Or was it something else? Because the platform itself doesn't actually allow the same field to be defined twice on the same table. Here are some related things that could be going on though.
1) A field can sometimes be added twice on the same form or form section. Some classes have business rules to try and prevent this but others do not. And through a variety of other means you can end up with that happening even on classes that try to prevent it.
2) You may have different fields with the same label but a different column name. In that case, someone has defined a custom field (or relabeling another field) with a label that is not unique. If that is the case you may have some work to do to determine which field is the one you want to use, how to move the data to the right field, and what to do with the field you don't want (or whether simply relabeling the field will help.)
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