I have submitted my blog (www.manilablog.com) to several web directories without any problems, then starting last week up to now several PHPLinkDirectory directories could not verify my blog anymore. The prompt was: The URL could not be verified, either the link is offline or the server could not be reached (forgot the exact word). My blog is not banned by Google, my other blogs hosted on the same server were submitted without any hitches, it is not offline.
Check the link in my sig, see if you can find an answer at their forums. I encounter it occasionally.