Im just using poisonmenu. It's not a Fubar related addon, it just gives a minimap button.
Even when i try the classic way to change/refresh a poison on a weapon wich already have a poison or other buff on it, im getting the error.
It could very well be a non Ace addon that does it as well. Taint is a pita to track sometimes.
I use oApplication and have no issues personally. Have you tried disabling Fubar and see if the taint goes else where? OR try the 50/50 method of disabling half your addons at a time in an effort to narrow down the culprit?
Nor do I have trouble with Poisoner. I agree with Cal here; taint is a royal pain. I'll give PoisonMenu a shot this evening and see if I have any issues, unless you are able to narrow it down before then. :)