- I've never seen it to be a shortcut. Somebody must have done something unusual.
- And I've never seen a folder refusing to accept files starting with certain letters, and no others.
- And I've never seen a backup causing such. But, then, I don't use any special backup program to copy files to an external hard disk. You don't tell how you did it.
So it's rather strange, all together. May I hope your backup is still complete? Better disconnect the external drive then until the problem is solved.