Delete the invalid one out of the folder under Objects where your project is saved. May also try cleaning the project under tools. Might be considered a tiny bug that B4A doesn't delete existing files regardless of their extension.
Remove Selected from the Files tab will remove the item from the project.
Another message box will immediately appear
asking if you would like to physically remove the file from the folder as well.
That message is NOT a confirmation for removing the file from the project.