If the object is saved, this error will not occur.
Related issues:
(1) In previous versions, pressing CTRL+S to save objects would save all objects.
(2) Now, if you modify two objects, both object labels will display an asterisk (*). However, if you use CTRL+S to save in any interface, only one corresponding object will be saved (only the asterisk for that single object disappears).
(3) Therefore, when you have modified two objects and press the shortcut key to save, as long as there are still objects with an asterisk on their labels, running the game will result in the above-mentioned error.
This issue appeared after the 2.0 version update. Since I couldn’t find the cause until now, it has been a source of confusion. But this time I finally caught it, so I’m posting it here. However, I don’t know whether this is a bug or a normal mechanism of the new version, so I posted it in the question section.
Hmm I’ve been trying to replicate this and can’t. Adding a child node and running without saving, with one or two unsaved objects, never showed the popup for me on 2.0.5.
From what I found, when you run with unsaved objects the editor saves them first, and that also rewrites scene_transition_data.tres. The error means Windows wouldn’t let it replace that file because something else had it open at that moment. I’m wondering if an antivirus or a sync program is scanning your project folder. If you use one besides Windows Defender, maybe try adding the project folder to its exclusions.
For the Ctrl+S part, Ctrl+S saves only the current scene and Save All Scenes is Ctrl+Shift+Alt+S. If you’d like Ctrl+S to save everything again, you can go to Editor Settings > Shortcuts, give Save All Scenes the Ctrl+S shortcut, and clear it from Save Scene. That should also keep the popup away, since nothing will be left unsaved when you run. It could also explain why it only started in 2.0, if you rarely had unsaved objects when running before.
Thank you, Mr. Baz, for your reply. I have replaced the shortcut keys.
As for that error popup, I’ll ignore it for now because I habitually save the object before running the game.
As long as the object is saved, the popup won’t appear when running the game.