SOLVED IT! And probably found a bug.
I started going into the new Dreamweaver toolbar icon "Preset Manager" and setting up all my presets BEFORE adding HTMLEditor to a textarea. And then when I added the editor I choose from one of the predefined presets directly in the wizard.
But when I create the preset from within the HTMLEditor wizard with the "Customize" button the preset seem to be working just fine without error!
Can you recreate that?
Thanks anyway Neilo and Jason for help and suggestions!