A blank page will usually be accompanied by a corresponding entry in your web server’s error log. Can you look it up and post it here, then I can see where to look for what the fix might be.
Is this about one bug, or two? You mentioned a blank page after saving details for a new user, and then “email wasn’t sending properly”. I am aware of a couple of possible issues that might cause the first, but nothing I (yet) know about regarding current email issues in kiwitrees.