Members directory pagination navigation problem

Hi -

Since upgrading to BuddyPress 1.5.5 and WordPress 3.3.1, we're seeing a problem navigating through pages in our Members Directory at http://northings.com/members/. The first page of members shows fine, but we get a "Sorry, no members were found." message when trying to move forward and back through members pages.

We have customised the Daily Theme considerably, so before updating the whole theme and reimplementing customisations, could you suggest what files from the theme might be the problem? Otherwise, the theme still works fine across the site.

Thanks
Marcus