I used the w3 validator on one of my sites, and it seems like almost all of the errors that it found were from the Google Adsense code. Whats the deal with that?
Well I'm not totally sure but if you used xhtml validator then it can't validate your javascript (I think adsense is javascript ?). It validates only your html.
if there are some error on the page with w3 validator, site can not work properly on different browsers.
W3C Validation should be taken with a grain of salt. I've seen many sites having 50 + errors and working perfectly the same in browsers. ie Google has been optimized to be as little KB as possible, and has alot of errors because of that.
W3C validator validates XHTML/HTML code, and adsense is pure javascript. I doubt thats what breaks your validation. I would rather say check if you have doctype at the very beginning of your code.
Take a short look at this link. Why would a page with less than 20 words on, and an image be left with 50 errors? And it's still one of the most visited websites. Is it ignoring the v3 stuff? Does the website look bad in your browser? Just asking
and If you see the source code it does not have a doctype, adding a doctype it will determine the parse mode and it will validate.
I know I was just pointing to Google's ignorance. Their business starts at www.google.com and the v3 trend does not seem to be affecting google in any way.