This little message was introduced in the last patch. Copied below from the Blizz website for the patch.......
http://www.worldofwarcraft.com/patchnotes/
If you get a message "Interface action failed because of an AddOn", this means that an AddOn interfered with the Blizzard UI in some way. To diagnose this, enter the following into chat "/console taintLog 1" and restart the game and try to reproduce it. If you reproduce it, you can quit the game and search through the file Logs\taint.log for the word "blocked" and mail the log to the author of the AddOn listed there. Once you have done this you can turn off logging by entering the following into chat "/console taintLog 0”
For more details on UI macro and scripting changes, see the UI & Macro forum.
Dunno if this helps in the specific case but it explains the message
