A Google Webmaster Help thread has a report that Google’s preferred domain setting section in Google Webmaster Tools is not working. When some webmasters click on the “Settings” link on the left hand side, they get a response from Google that says “oops!”

It works for me, personally, and for many others:

But for this webmaster and some others, it is not working.

Susan Moskwa from Google has confirmed the issue and said a fix is underway. She explained that due to the holiday weekend, it might take a few more days to fix than a typical weekend. She said:

Again, I personally was able to access the settings section and even set a preferred domain for a site, as a test.

Forum discussion at Google Webmaster Help.