Specifically, Night Fae, I can't verify if it interferes with others. Sometimes after doing missions, this addon seems to block deposits into the reservoir. Resolved easily enough by a /reload, though.

I get this error as well... but it is not always Covenant Mission Helper than is the culprit. It seems to be something with the way that WoW handles add-ons and keeping them all in their own little box.

I've had this error before saying Tom Tom or other add-ons tried to perform an action but it was blocked. Also had it pop up with other add-ons (Garrison Mission Manager for example... but non-mission table add-ons as well).

(Side note: The worst thing is when you get it in combat and suddenly you are struggling to use hotbars and / or macros.)

Still get this error from time to time ... /reload ui fixes it for the moment but not permanent. At least I can bring my anima to the reservoir that way.