Catalog Import throws "sql duplicate key error" although overwrite option is set as "true"

When we call to Mediachase.Commerce.Catalog.ImportExport.Import method in order to import one catalog from an xml file , we are getting an Sql error regarding "Violation of Unique Key" but it shouldn't happen because we set the method param "overwrite" as true.

Error Number:2627,State:2,Class:14
System.Data.SqlClient.SqlException (0x80131904): Violation of UNIQUE KEY constraint 'UQ__#B5DEE65__C86C24AB46D15906'. Cannot insert duplicate key in object 'dbo.@ContentProperty'. The duplicate key value is (101, 1, <NULL>, 17, en).
The data for table-valued parameter "@ContentProperty" doesn't conform to the table type of the parameter. SQL Server error is: 3602, state: 30

Any comment or direction will be appreciated.