It doesn't really confirm it, as it's a default message whenever a Note is unavailable. The same message would be displayed if they completely retracted the Note, never to be available again. However, the majority of the time it means just what Cristiano said, that it's in the process of being updated to a new version. I've complained to SAP before that it would be better in almost all cases to leave the current version available during the editing, and they've agreed, but this is still how their system operates.
Usually it is re-released within a day or two. However, if a few days or more go by without it coming back, then the thing to do is to submit a Customer Incident to the relevant application area of the Note, as probably someone "checked out" the Note to update it, then got distracted by something else and forgot it. If the Incident doesn't work, try tagging a space editor or moderator here, preferably one who is an SAP employee, and see if they can raise the issue internally.
Cheers,
Matt