Error 8101 An explicit value for the identity column in table can only be specified when a column list is used and IDENTITY_INSERT is ON

When you try to insert rows to identity column , you should include set identity_insert is ON 

SET IDENTITY_INSERT Table_Name ON 
GO 
INSERT INTO dbo.Table_Name ( col1, col2, col3) 
SELECT col1, Col2 col3 FROM dbo.Table2 
GO 
SET IDENTITY_INSERT Table_Name OFF 
GO