I did it again now.
I restarted my laptop, I copied and pasted the code in again.
But it's still ejecting a runtime error '5937'.
It's marking this again:
i.Range.Characters.Last.FormattedText = wdDocSrc.Range.FormattedText


Furthermore it's collecting all files from the first subfolder twice in the active document.
But it's collecting none from the files in the secong subfolder.