I just uploaded a small update to this script. I'm not convinced that it will address the issue you reported, but the 'dlg' variables now conform to better programming conventions.
Viewing post in Aseprite Script: Amiga OCS/ECS Color Palette Mixer comments
Thanks for your fast reply and fix. I tried many images and for now i don´t get the message. It works fine now. Thanks!
A question:
Ist there a way to pick colors while the color dialog is open? When not, maybe get the current selected color from Aseprite? It would be eayser to adjust colors..
This is just a minor thing, bigger adjustments are done later in Deluxe Paint ;)