First, please forgive the necro thread but this was the exact issue I was dealing with recently and didn't want to make a new thread for my findings.
I was having a hell of a time figuring out why poison (the spell) was not working as it should. I was experiencing the exact issues that Van Glan Bloom was reporting-- the target would receive the poison spell, it would then "tick" and the poison would be gone from the target without them having taken any damage.
After a bunch of testing (tested different spawn types to see if there was a consistent theme as far as what would get damaged by poison and what wouldn't), every target would get poisoned, and upon the first tick of damage, it would say "*<mob name> is (null)*" and the poison would wear off. Every now and then the target would receive a huge amount of damage (Largest I saw was well over 60,000), the poison would wear off, and the target would still be alive and at full health even though I just saw them take damage of the aforementioned value. All of this was happening with no errors showing up on the console, mind you.
Then I came upon this thread. I saw Criminal's post about the Layer= information, compared what was in my version of the sphere_spells.scp and found that that line was NOT missing from my script.
I was just about to post seeking help when I decided to compare the two poison scripts line by line.
Code:
EFFECT=0 // 100,750
is where my problem was. Mine is set to
Code:
EFFECT=100,750 //Only used without Magicf_OsiFormulas
OK, so I checked sphere.ini to see what my settings were for Magicf_OsiFormulas, and sure enough it was turned on. I turned it off, resync'ed the server and tried to poison something else. This was the fix.
Sorry for the wall of text, but hopefully this might help somebody out in the future.