Zoltar,
You may have the Accessories add-on installed but do you also have the Accessories library parts loaded.
Without thes the add-on can't do anything.
Also I have never known the check doubles add-on to check for doubles at startup - maybe I am missing something.
I have only had it check when I manually tell it to.
I just re-read your post and you mention double "library parts".
This is a function of the Library Manager and is not controlled by the add-on.
The Library Manager is telling you that you have two or more libraries loaded with the same library parts in them.
Or maybe you have duplicate files within the one library.
Clicking on the "info" button should give you more details.
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11