Lisp problem
That TEDIT routine describes itself as being made to compensate for the fact that the TEDIT command had disappeared in Acad2004. That AutoCAD command is back in 2016, so since the name is the same, just use that [or, if you've been set up to load the AutoLisp version and replace TEDIT with it, remove that loading/replacing from your Startup Suite or acaddoc.lsp or wherever it's coming from].
As for the Add-a-line routine, I'm going to suggest you use MakeMore.lsp with its MM command, available here. If what you select is ordinary Text, it offers you the option to either make a New piece of Text anywhere you choose, or [what you would choose in this case] to Continue from the selected Text on a line below, which it appears is what A2T does. But MM doesn't make a copy of the Text and leave you to edit it [as it appears A2T is meant to do, though it didn't work for me either], but starts another line for you, fresh below it, just as if you had just typed the selected object and hit Enter for a line below, and you can just starting typing the contents, and continue for as many additional lines as you want.
[MM has a lot of other enhancements over ADDSELECTED, which didn't exist at the time -- see the comments in the file.]
@EgoonS wrote:
... the other problem I had is this lisp (Copt text edit, supposed to be uploaded in my first post. Thanks
The DDEDIT command seems to have disappeared in recent versions. Try changing that line to:
(command "_.textedit" "l")
