why validator and Google giving 404 error

I am trying to check some validation, speed, etc. When I run the validator at websiteoptimization.com, it gives a 404 error. Now I KNOW the site is up, I've got customers on it. Can anyone suggest why this 404 error is being returned?

I'm not sure if this is related, but Google has been giving a "**We can't currently access your home page because of an unreachable error." ** error when I check my activity through their webmaster tools. Consequently, they have DROPPED all my new Zencart pages.
This problem commenced sometime after updating to 1.3.02
The site in question is in my sig.
Can anyone help me with this? My traffic is taking a nosedive. And my orders...
Thank you in advance

It seems to be an across the board problem. When I try to submit the site here: https://siteexplorer.search.yahoo.com/submit it tells me the site does not exist. So somehow the site is returning a 404 error? Please help, and/or point me to the tools to troubleshoot.
Thank you

Okay, found it, I think. In this thread, http://www.zen-cart.com/forum/showthread.php?t=39595 I followed the advise to add this to the init.sanitize.php page:

Around line 105 of includes/init_includes/init_santitize.php, find
if (!is_dir(DIR_WS_MODULES . 'pages/' . $_GET['main_page'])) {

add this line below it:
header('HTTP/1.1 404 Not Found');

This one work for google HTML FILE verification

This DID get my Google html file validated, but it also rendered a 404 to the world. So I have removed it, I am now again being seen. I suspect the Google 200 problem will return.
The chicken and the egg...
If anyone has any ideas on how to solve all this, please do tell!