34000 404 errors URL in Google webmaster

Hi, I am receiving more than 34K 404 errors on my site in google webmaster
while the url’s shown by Google do not exists throughout the website. My traffic goes down to half of previous traffic…What can i do?

Here are some of the links and screenshot of the error I am unable to analyze why these issues are occurring

URL 	Detail 	Linked From 	Detected
http://www.cheapmonthlymobile.co.uk/3Mobile-Mobile-Phones/Apple-Mobile-Phones/Apple-Mobile-Phones/Blackberry-Mobile-Phones/BlackBerryCurve9300MobilePhone.asp
	404 (Not found) 	2 pages 	Jan 28, 2011
http://www.cheapmonthlymobile.co.uk/3Mobile-Mobile-Phones/Apple-Mobile-Phones/Apple-Mobile-Phones/Blackberry-Mobile-Phones/Digital-TV.asp
	404 (Not found) 	2 pages 	Jan 29, 2011
http://www.cheapmonthlymobile.co.uk/3Mobile-Mobile-Phones/Apple-Mobile-Phones/Apple-Mobile-Phones/Blackberry-Mobile-Phones/HTC-Mobile-Phones/HTCWildfireMobilePhone.asp
	404 (Not found) 	2 pages 	Jan 26, 2011
http://www.cheapmonthlymobile.co.uk/3Mobile-Mobile-Phones/Apple-Mobile-Phones/Apple-Mobile-Phones/Blackberry-Mobile-Phones/Mobile-Networks/TMobilemobileDeal.asp
	404 (Not found) 	2 pages 	Jan 31, 2011
http://www.cheapmonthlymobile.co.uk/3Mobile-Mobile-Phones/Apple-Mobile-Phones/Apple-Mobile-Phones/Blackberry-Mobile-Phones/Mobile-Offers/Free-Xbox-360-Elite-Mobile-Deals.asp
	404 (Not found) 	2 pages 	Jan 26, 2011

Do you really have “Apple-Mobile-Phones” as a subdirectory of “Apple-Mobile-Phones”? Does your directory structure look anything like that? Can you see any links to those pages when you look around the site?