Just a heads up but prepared invasions are still utterly broken balance-wise. It's easy enough to avoid using them as a human player but the AI still burns up all it's prestige, manpower and Norse moral authority on pointless invasions that give 1-2k extra men against a coalition of all of Western Christendom.
Might be best to disable them until they can be better tweaked.
Can you give us more detail? Who are you playing, which bookmark, and who are you attacking, etc. We tested it before we released and found it to be mostly balanced.