IDENTITY_INSERT

Problem:
An explicit value for the identity column in table DB1.dbo.TABLE; can only be specified when a column list is used and IDENTITY_INSERT is ON

Solution:
1) set identity insert to ON:
SET IDENTITY_INSERT db1.dbo.table1 ON

2) specify column list, for example:
INSERT INTO
DB1.dbo.TABLE (column1, column2, column3)
SELECT column1, column2, column3
FROM dbo.TABLE1
dbo.TABLE2 ON dbo.TABLE1.column = dbo.TABLE2.column