Google upgraded the publisher center over the past couple weeks but not everything in the new publisher center seems to be working properly. A Google Publisher Center Help thread says that when you try to add a new section using the web crawl option, it simply doesn't work.
Chris Andrews said in the thread "If I enter a url from any of the sites I work with, using a category on my site rather than an rss feed, nothing seems to render. I get the message: There are no items to show."
Here is what the form looks like, it looks like they changed it a bit since Chris posted about this:
Chris later on said "I see they have now removed the 'web' crawl option when you go to enter a section, hopefully they are working on that and it will be back." That was two days ago, but I do see a crawl option now, so maybe this is now resolved?
Have you tried this?
Forum discussion at Google Publisher Center Help.