This basically means that you have modified the structure of a custom section that is being denormalized. The custom section is mapped to a specific database table and the schema has changed, so the table has to be recreated and re-denormalized.
This is done via a database script, DENORM_GEN_DLL, which should be executed by your DBA. This script would remove the existing table and recreate it with the new structure, and mark if as ready for denormalization. The Denorm process can then be run to take any existing data for that custom section and import it into that table.
You can read the details about this in the Custom Section Denormalization guide in the Extensibility Pack(s).