Thanks @SirriS_RU for updating the file. Can confirm it works again. I updated this thread's title and added a note to the initial post.
Still no luck, I deleted everything in %localappdata%\Microsoft\Windows\INetCache\IE
Uninstalled the client, downloaded the 64 bit client and reinstalled, did the renaming, copied client.swf (and "unblocked" in the file properties) but still got the same message.
I'm not too bothered since the Unity client is tolerable for me, but it's an interesting hack. Good work SirriS_RU.
Follow the instructions on wiki, it worked for someone I know
Copying the client.swf from the .rar file on Wiki worked. I guess my browser must have been serving me a cached version of the client.swf from SirriS's link.
Works for me, thanks for this post (and to Sirris_RU).
I am getting this error: https://prnt.sc/1qtisrr
What did I wrong?
Looking forward to an update