all of my sites were verified by google and a month ago i was shocked to see in my dashboard that all my sites were unverified.so i again started the procedure to verify them but whatever i try it says "We've detected that your 404 (file not found) error page returns a status of 200 (Success) in the header."and even i can see the uploaded html file through google link.eg. I've uploaded the file to http://www.xxxxxexamplexxxx.com/and can view http://www.xxxxxxexamplexxxxx.com/googledxxxxxxxxxxxxx.html bin my browser. i have tried both methods uploaded HTML file and added a meta tag to my site's index file but it still does not resolve the issue it seems that there is some problem with google algo.
It seems you're not reading the message Google is giving you. You can upload any file you want, but THIS is the problem you need to fix. Did you maybe redirect all 404 traffic to your homepage or something?