We keep getting blitzed with 404 crawl error messages in webmaster tools Our web developer wanted to pop a custom 404 response page in there that would re-engage visitors to the site but apparently it's not a function Deco can deal with
404 has nothing to do with "incorrect code" - it simply means "page not found". In other words: you have a bunch of broken links or incorrect paths.
Without HTML source code to peruse, it's very hard to determine what the error is.
Make sure all your page references are correct (<a href="/path /to /file.html"... >) without the spaces that Yahoo! requires). See to it that there's no reference to any "C:\Documents and Settings..." stuff.