Cannot Add Alternate Recent Posts Widget to SIdebar

I was just wondering if anyone else was having a problem adding this widget to their sidebar on the Widgets page (In the Appearance section).
When I go to add it, all the other widgets disappear, and only this widget box remains with the edit tag, along with the show all widgets box on the same side, and the show sidebar box on the other side. Everything else disappears, and when I hit the edit button it gives me the message about my changes not being saved. It just doesn’t work for me, perhaps it’s conflicting with another plugin.