Why would i get a duplicate write error of auto-generated primary key?
I think this could happen only if manual intervention was done to that primary key. It's possible to manually insert data in the identity column only if option "set identity_insert table_name on" was used, that way you can generate PK errors.
But better check exactly if the PK is only that identity column, and, if yes, if this option is used in any of the stored procedures or scripts that you use.

SQL Server alone would not have any reason to not treat correctly these columns.