I just discovered a footnote in the Twitter documentation stating that "near:" can't be used when searching from other programs. And because "within:" can't be used without "near:", both are prohibited.
In the next version of NodeXL (220.127.116.11), the following message will be displayed:
"Although you can use "near:" on Twitter's own search page, Twitter doesn't allow it to be used when searching from another program, such as NodeXL. Remove the "near:" and try again."
Thanks for reporting the bug.