When trying to cast any Mage Portal or Teleport spell, the error pops up: "EnchantMe has been blocked from an action only available to the Blizzard UI. You can disable this addon and reload the UI."

I am currently on v1.3.6, updated 21 hours ago as of time of this post.

Any specific steps to consistently reproduce this error? It works fine for me. This addon does not touch the action bars to interfere with casting portals.

There is a bug in the game since DF which causes this to happen rarely and a random addon gets blamed. I've had this error blaming WeakAuras, Raider.IO, Mount Journal Enhanced and others.

Try disabling Enchant Me for a while to see if it happens again and maybe a different addon will get the blame haha.

This addon is not doing anything special except attaching the indicators to your equipment frames, which many other addons do the same way (e.g. Simple Item Levels).

It's likely the issue with an (at this point old) UI taint bug I mentioned before, but if it stops happening completely with Enchant Me disabled that would be a cause for suspicion.

Hmm, okay. I've poked at stuff a bit more.
Created a new character (for other reasons) and ran it through Exile's Reach until Re-Sizing the Situation. I used the Re-Sizer through the default Quest Objectives pane on the right, then hit this error. It would repeatedly happen each time I tried to do this. Tried to right-click the boar itself to activate the Re-Sizer, and it started to work with no error. Odd. Logged out, switched characters (to the original character that got this warning on) and couldn't reproduce.

(Originally, error happened when trying to use my own port out of Dustwallow Marsh, one of the Radiant Echoes event zones.)

After trying on the original character, I switched back to the new character, and it didn't error. Fully exiting the game and re-entering doesn't let it error anymore.

I'm so confused.