Validator warning, but no messages

I want to validate my website, but in the error report it shows that I have 1 warning, but it doesn’t show what warning.

Am I doing something wrong?

Yes it does show the warning:

Using experimental feature: HTML5 Conformance Checker.

The validator checked your document with an experimental feature: HTML5 Conformance Checker. This feature has been made available for your convenience, but be aware that it may be unreliable, or not perfectly up to date with the latest development of some cutting-edge technologies. If you find any issues with this feature, please report them. Thank you.

So what is the warning then?

Exactly what Stephen posted

HTML5 is not officially ready yet, so the validator is not prepared to assure you that this is valid HTML5. Just ignore this message.