It seems that loads of peeps who had their interviews scheduled around this time have had theirs cancelled (mine included!)
As far as I know no one has been given an explanation for it, just advised that it was "unforseen circumstances". Mine has been rescheduled for the 20th of this month (eeek) but trying not to get hopes up too much in case it changes again.
Have you had any more word on when yours will be?