Someone change my permalink

This situation happened twice, I hope someone can help me fix this problem.

My blog is http://edblog.net

I create a custom URL structure for my permalinks and archives.

Like this http://edblog.net/archives/500

Few days ago, someone change the permalink, only index is normal. Other pages are become a blank page the content only show http://edblog.net and a smile.

If I use http://edblog.net/?p=500 it’s normal
but I use http://edblog.net/archives/500 it’s not normal.

After I reset the permalink, this problem is resolved.

Does anyone have the same problem ?