Yeah, I'm having the same problem too. I click on V12.1sp1 on the download page and it sends me to a "download.altera.com" address, which is a completely invalid URL, and the screen it displays tells me exactly that. Intel support, in their infinite wisdom, said that I should go here to find the solution to my problem. Now, you tell me, who on this list of users is going to be able to fix an "Invalid URL" error for me?
Seriously, you forum guys can be a big help at times, but Intel just blowing off my direct complaint, and suggesting that I post it here, is just plain LAZY on their part. You would think that this is the sort of thing they would want to know, but..... Nooooo. I predict that this will remain a problem for a very, very long time.
I.am.outta.here. Intel doesn't pay me enough to do their work for them.