Lexica is talking about the spells which are being lowered because of domains. Healing domain takes the 3rd circle Cure Serious Wounds and makes it a 2nd circle Cure Serious Wounds. However, since a level 3 doesn't know the 3rd circle, they're being prevented from casting it, which is an error.
Even if this is fixed, be aware that after this update goes through, the default behaviour of NWN disallows you from spontaneously casting Cure Serious Wounds as a level 2 spell, at least if I remember correctly. You have to prep it. I got into the habit of having at least one as a result.
You also can't cast non-Cleric spells from scrolls even if you have a domain that grants it. Dunno if that's intentional.