I have successfully upgraded two blogs on my website to version 2.3 - Great!.
However upon creating a third (new) blog installation on the same host if fails during logon to the administration module. The install itself was successful.
The logon error is:
ERROR: WordPress requires Cookies but your browser does not support them or they are blocked.
This message is returned either by providing the correct credentials or wrong ones (and cookies are supported).
The logon for the two other blog installations works fine.