900 "not found" errors in first 36 hours....yikes!

First read what the log says and accessing the URLs, together with debug, try to locate the error.
The most common error in configurations is with URL replace: www.sakic.net/support/faq/sef_advance/#19

i'm getting the same problem here, i checked my logs, the component is rewriting the urls but when i click the link is going to 404, only making aliases is working

You should also check the FAQ, this one in particular: www.sakic.net/support/faq/sef_advance/#19

Emir, thanks, firts i checked i didn have so many replacements, second chance you said i checked and it aws a "," i deleted and now is working,thank you for your help
;D

Hi Emir

It would probably help if the 404 errors were sorted by occurence.

Currently its hard to wade through 100s of URLs without knowing which ones are urgent.

Yep - 2 days of not checking the 404 logs and there are over 1500 errors logged, nearly all from spammers but probably a couple of genuine errors in there. Mostly its stuff like this:

  components/com_joomlalib/?baseDir=http://www.######.se/components/com_extcalendar/ec.txt?
search.php?cutepath=http://www.asoc-posidonia.es/pr.txt??

Without listing by the number of times the error occurs, the log is unusable.