Hi Simon,
I no longer remember how SDM 12.6 works in this area . . . it maybe has been renamed in the current releases.
What's it trying to do? Is there an Incident Template in existence? (When it works on test?) If so, have a look and make sure that everything on the original Incident/Template "still exists." So for example, if it uses a particular Status, then that Status should still be present and Active.
Worst case, you can run pdm_trace against the spelsrvr (and maybe web engine and domsrvr, but mainly the spelsrvr I would think) and see if it passes the same thing in the working versus non-working scenarios. You should be able to find the same error in the pdm_trace output, and then work back up the page until you find a difference where one of the fields is empty/different, and then that would be key to check.
Kyle_R.