In short, under the "Then narrow your results by..." options are disabled for some. When you click on them, they do not work for users. I am not sure what the issue is, but users are reporting it not working in all browsers, including IE, Firefox and Google's Chrome. I tested it myself in Chrome on a Mac and it works fine.
Google's Kousha said that he will escalate the issue, being that there are enough reports of issues to warrant someone to look into the issue. Kousha wrote:
I've heard from multiple users about this issue, so I'm going to escalate the issue and check back with any updates.
Forum discussion at Google Web Search Help.