The 8th level Druid spell "Fire Stag" summons an animal that leaves a flaming trail/"Wall of Flame" behind. Unfortunately, this trail produces an error message in the combat log:

 

 

Note that this does not affect the Wizard's Wall of Flame spell.

 

To reproduce, level up the Druid, enter combat in one of the adjacent rooms, summon the Stag, and run it around the enemies for a bit.

 

Save game:

 

https://www.dropbox.com/s/i98l0ht4o435vqu/67c5419fad4745c3ac4b721bd0b4b631%207844429%20TempleofEothas.savegame?dl=0

Same issue for me.

The issue persists in 3.03.