MS SQL server does not allow inserting explicit values to IDENTITY columns. It can be done only if IDENTITY_INSERT is set ON for given table. Unfortunately, according to https://msdn.microsoft.com/pl-pl/library/ms188059(v=sql.110).aspx:
"At any time, only one table in a session can have the IDENTITY_INSERT property set to ON".
So, when more than one table with identity columns are edited or copied, then there is no way to insert rows.
It could be solved by (optional) sending SET IDENTITY_INSERT ON statement before inserting row(s) and SET IDENTITY_INSERT OFF after inserting.
Especially DB Copy suffers from this SQL Server "feature" - multiple table copy is not possible.
