Yesterday we reported there were issues with verifying your site in Google Webmaster Tools. The issues were around using the META tag verification, but that is now resolved, as of yesterday evening.
Googler, Susan Moskwa said in the Google Webmaster Help thread:
We're rolling out a fix for the meta verification issue right now, so this issue should be resolved. Please give it a bit of time to roll out fully, and then if you're still getting the "We've detected that your verification file returns a status of 404 (Not found) in the header" error when trying to verify by meta tag, please post back here.
If you're getting any other type of verification error, please search the forum for an answer, and start a new thread if your issue hasn't been answered/resolved.
Soon later, webmasters began to report that it was now working. In fact, the person who initially reported the error said:
I think I was the originator of this thread - and this is just to say that Meta tag verification worked OK for me this morning.
Thanks to Google for fixing the problem.
Forum discussion at Google Webmaster Help.