You need to make very sure Ancillary actually exists with exactly the same case _ and spelling and has appropriate references to descriptions and .tga - wonderful gizmo for testing that traits and ancillaries don't cause crashes is here:
https://forums.totalwar.org/vb/showthread.php?t=68697
unfortunately what it doesn't do is tell you if trigger conditions are actually valid (I've managed to add many that don't crash but don't work either) or if trait / ancillary effects actually work (again I've found some inc. vanilla that don't seem to do what they are meant to, LOL)