Sql-server – Errors in the OLAP storage engine: A duplicate attribute key has been found when processing

sql serverssas

When I try to process my cube and specifically the Employee_DIM, I get the following error :

Errors in the OLAP storage engine: A duplicate attribute key has been
found when processing: Table: 'dbo_Employee_DIM', Column: 'Firstname',
Value: 'Aurélie'. The attribute is 'Firstname'.

I think that duplicate values for the column Firstname are considered as keys. After checking with the Employee_DIM : 

 SELECT [Firstname], COUNT([Firstname]) AS dup_count
     FROM [Database].[dbo].[Employee]
        GROUP BY [Firstname]
             HAVING (COUNT([Firstname]) > 1)
                ORDER BY [Firstname]

enter image description here

Is there any alternative to leave only the business key in Employee_DIM and get Lastname and Firstname without adding them in the dimension for a future use?

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