Ok, simple enough to fix: we just need to do what the error message says and SET IDENTITY_INSERT ON for both tables:
SET IDENTITY_INSERT dbo.User_DEV ON; SET IDENTITY_INSERT dbo.StupidQuestions_DEV ON;
And… it still didn’t work:
IDENTITY_INSERT is already ON for table 'IdentityTest.dbo.User_DEV'. Cannot perform SET operation for table 'dbo.StupidQuestions_DEV'.
Click through for the ramifications and your alternative.