@Vagulus wrote:
and none of them are locked.
Actually, your screenshot shows that the currently active Representation (Master) is locked. For the purposes of this message, the currently active Representation is the only one that matters.
The "Master" View Representation is automatically locked, and can't be unlocked. You most likely did something like what @admaiora mentioned (section view). Section views are saved as part of the View Representation, but since you're using a Representation that by definition can't be saved, you are getting the warning. It is not saying that your file isn't saving - it is the changes to the View Representation that are not being saved.
You're probably stuck with the message until you close the file and reopen it. When you do, the section view (if that's what you did to trigger the warning) will be gone, but so will the warning message.