every page creates a 404 error

hi, i have a site running with wordpress 3.0.1

when i create a post e.g. http://www.hiphopdance.gr/2010/09/30/
google bot indexes it. That’s ok, but when i go to webmaster tools, i see that a crawl error exists. the problem is with the author. For example, http://www.hiphopdance.gr/2010/09/30/author/admin
Googlebot indexes the above uri but it can’t find it.
this problem occurs to every post i make. What should i do? because this is an overkill for my site…