Google recently improved the Webmaster Tools "message center" by having messages wait for you even if you are not verified.
But a few reports are coming from Google Groups that the message center is not displaying open messages. Users are seeing they have a message, they click on the message and are presented with the following error:
Your messages are not available at this time. Please try again later.
Google Webmaster Trends Analysts, Jonathan Simon, responded saying:
This appears to have been a temporary issue.
But another user came in an hour or more later saying that he also just received that error.
I was unable to verify or replicate the error myself, because I don't have any messages waiting for me. Google, want to send me a note so I can test it? ;-)
Forum discussion at Google Groups.