Do not ignore duplicate key errors.

http://technet.microsoft.com/en-us/library/bb630297.aspx

Do not ignore duplicate key errors. Change the KeyDuplicate property of the error configuration so that it is not set to IgnoreError

This rule analyzes the error configuration settings of dimensions to determine whether the KeyDuplicate property is set to IgnoreError.

 Best Practices Recommendations

Although the default value for KeyDuplicate is IgnoreError, you should not ignore duplicate key errors. If you use the IgnoreError setting, it can be difficult to detect problems with incorrect key columns, incorrectly defined attribute relationships, and data consistency issues. Instead of using the IgnoreError setting, it is typically better to correct your design and clean the data.
The IgnoreError setting can be useful in prototypes where correctness is less of a concern. However, you should change this setting after prototyping is complete to ensure data consistency.

 For More Information

For more information about error settings, see Processing Options and Settings in SQL Server Books Online.