If you notice, the Action, Labels, Common, and Variables menu items are all grayed out. This is an indicator that there is an issue and you will get the error. When I see this, I will close out the action, and reopen it, and it will resolve the problem. It seems that when the action opens, those components aren't loading, so the action things the Action Title is missing, which is why it's throwing the error.
sometime, it is also internet browser problem. It happend to me, that some action should be configured twice, because if the nice behaviour of the browser.
Maybe you can only check the issue in other browser or update to the newer version of NW.