The computer returns an empty error with a callstack.
Tested on a fresh 1.12.2 forge 14.23.5.2860 and also on FTB Ultimate Reloaded.

Same for me, happened when I tried to install MineOS through Pastebin.
I'll try to investigate more later.

After a bit of debugging, I saw the following reason from internet.lua : "Server returned HTTP response code: 403 for URL: https://pastebin.com/raw/icKy25PF", which in other words means a forbidden connection. I don't know why no reason has been displayed, but at least now you know why Pastebin doesn't work.

Okay, thanks for your research!

I found a potential fix : make pastebin.lua send a custom user agent to impersonate a browser. Maybe OC is forbidden because it is recognized as a scraping tool ?