2
You are using a custom template set. So delete via the Template Set Manager every template for the forums in your template set. Then in the Template Set Manager you'll have a generate link for the forums for your template set. Generate them and it will be alright. You'll possibly have to do this type of thing every time you update to new version of the forums.
BTW, those 3 files would still show as missing but don't bother about them. It's not really a bug.