There are actually a number of events marked DON'T USE. The one in Diamsecr just doesn't work at all, and it didn't even work back in JJ2 v1.00, so it's been a long time since it did anything. I would guess it was some sort of sign post, but I obviously can't be sure.

The other two events you might sometimes see as DON'T USE are Trigger Zone or SP Airboard. Download an updated jcs.ini file from J2O or some other site and see if that helps at all.