[Plugin: Advanced Recent Posts Widget] Widget won't stay in sidebar

I know this is a repeated comment, but the last one didn’t seem to be resolved. This is with WordPress 3.3.1 and with a highly customized version of the twentyten theme. I try to add the widget to my sidebar, but when I view the page or refresh the widget admin page, the widget disappears.

http://ww.wp.xz.cn/extend/plugins/advanced-recent-posts-widget/