This happens to me sometimes. This is what I do:
1. Widen or lengthen the page margins in the tools section of the editor to see if you can get the box to show.
2. Sometimes you can right click and view the HTML and find the offending box as well.
3. If all else fails, call support and they can remove it.
4. Or, re - do the email if you think it is quicker than calling support.