Larian Studios Forums Divine Divinity (English) Help/Tips/Tricks all resistance down to -524486 - HELP

Try unequipping and re-equipping anything with a resistance bonus. Does that fix it, or do your resistances just go negative without the equipment?
If necessary, you could use iZakaroN's SaveEditor (or from Kiya's site, with description) to remove any points in Magic Barrier, then learn/re-learn the skill in the game, save and repeat as required.