I upgraded my store from 4.1 to 4.3, then added the Emporium theme which was an upgrade from Traction 4.1.
The SS_JC_JCarousel table did not have the ID column as a primary key, and it was not set with IsIdentity. So when I went to add a new JCarousel to my site, an error occured:
SqlException: Cannot insert the value NULL into column 'Id', table 'mydb.dbo.SS_JC_JCarousel'; column does not allow nulls. INSERT fails.