404 errors and related issues

Hi there, firstly I want to say that I am a really big fan of this plugin.

Lately however on one of my sites I found one user (someone I know) being locked out. When checking the logs I see it is pointing to a file that does not exist. Any idea how I can go about resolving this?

I also notice quite a few 404 errors on my sites. For example my 1 site, has 624 while the other has 340. I’m really not sure whether this is normal or not? When should I be concerned? No one except the one person has been locked out so far, but I’m worried about the amount of errors.

Appreciate the assistance.

http://ww.wp.xz.cn/extend/plugins/better-wp-security/