I just duplicated a vertical arrangement and renamed it. After renaming an error is coming Error from Companion: Source and target classes must be identical
Then I checked the components. And I noticed that the screen name has changed to the component name which I have renamed.
I solved that problem by adding a new screen and copying all the components and blocks from the old screen to the new screen. But I want to know why this error is coming?
So, clearly a bug, but finding it's root is very difficult. I assume that if you repeat the action of duplicating a vertical arrangement in the new Screen, the error does not occur?
It is possible the error is in an extension. However, I can't check your project, I get an immediate "Server Error could not upload project. Please try again later".
Are any extensions used for that specific Screen?
Are any of the extensions recently introduced i.e. not tried and tested over a considerable length of time, such as Taifun's extensions?
...when you open your Project, do you see a message similar to this: "An internal error has occurred. Report a bug?"
The Blocks work area for the BuyAndViewShopItems is empty and the App Inventor display of the in-work-area items like the bin, zoom btns etc are all in the top-left corner. This does somehow iron itself out but, well, more than disconcerting. The warnings on two Blocks are also wrong, though this is a known problem and nothing to do with the main fault.
Is this the "bad" version of your project or the "fixed" version? Either way, it might well be safer to start a new project from scratch.
I notice that there is a lot of discussion about the Custom Dialog extension. Ensure you have the latest version. Developed for Kodular, it might not be 100% compatible with App Inventor.
Thank you @ChrisWard, I have created a new screen and copied all components to that screen.
Now my problem is over. But that bug is still there in the old screen.