The formula for the Spell Spirit Ward is mapped to icon_formula_r_03_09_11.png - which is a resource (cooking spit) rather than to icon_formula_s_03_09_11.png (spell) ..
Interestingly, icon_formula_s_03_09_11.png is missing from my resources dir, but I have a new one that I designed for the same spell in my override dir - however that may well be that I inadvertently deleted it in all my tinkering with the icons.
In the event that the original has in fact been lost - I made a new one here that matches the others in game for you to use.
Additionally, it has been named Spirit_Ward (with an underscore) compared to Spirit Ward (normal convention for other spells).