The problem may well be that the layout objects you are trying to copy contain some corruption, which is causing the crash.
The message that the file was not closed properly is standard following a crash/improper closing of the application; when FMP closes a file properly, it resets a flag in the file as it closes it, and if that file-level flag is not "closed" when the file is next opened you get that warning. Usually it means nothing more than that the program crashed, but it is there to remind you that the file as gone through a bad experience and something might have happened to it.
Do a lot of backing up as you rebuild critical stuff. Once I know there is likely to be crash risks, I tend to do a manual backup script just before every high-risk operation, and routinely roll back to a copy of the previous backup any time there's a crash.
Thanks. I am trying to do that. Now, it happened as I used the command-Copy on some elements. I did not do the 'select all' but have been doing individual bits. Doing okay until this element. Perhaps they are the corrupted ones.
I have seen corrupt in a layout like this. Try copying parts of the layout and see what happens. Keep doing it until it crashes, then you know you have copied the corruption (or part of it). Try to copy everything else.
In reality, whenever I have a corrupt layout, I don't want to keep it anymore. So I rebuilt it manually.
Sounds very annoying, and requires much patience. To avoid having your new file crash as well when FMP crashes, I suggest you don't open it at the same time as you have your old file open. Use the process: open old file, copy stuff, if the copy process induces a crash, open source again, copy less/something else, if there is no crash close old file, open new file, paste.
since it crashes on copy, you can't examine the Layout XML on the clipboard ( e.g. with Clip Manager )
run a Consistency Check and a Recover, and check the log for any items "changed"
also, try working with a different OS, e.g. Windows