A couple days ago we reported about a widespread Google AdWords bug impacting the AdWords Ad preview and diagnosis tool.
I am glad to report, that as of this morning, Google has confirmed they have fixed the issue.
Google's Kathleen updated the Google AdWords Help thread saying "this issue has been resolved."
Google wrote this message in several threads complaining about the issue:
Hi All, Yes this issue has been resolved! Thanks for your patience!
I have yet to see confirmations from advertisers that it is working, but I have stopped seeing complaints.
Forum discussion at Google AdWords Help.