There have been some API changes in OSM some months ago, which caused OSM History Viewer to fail with NumberFormatExceptions on all changesets where something was deleted. This basically meant that History Viewer had been unusable for several months now. The issue is now fixed.
Discussion
Comment from SimonPoole on 4 March 2013 at 11:56
Thanks!
PS: could you change the data licence to ODbL?