I'm having the same error with Opus 12.26 behind a corporate proxy. Can it be that the issue is that Opus only supports HTTP proxies, but not HTTPS proxies?
Correct, HTTPS proxies are not currently supported and the update checker won't work through one. We looked into adding support, and may look again in the future, but there are several different and incompatible types of HTTPS proxy as well as autoconfig methods of discovering them, and the way they work from the Windows API, and how to set one up as a test environment that'd be equivalent to what enterprise networks really use, turned out to be both complex and poorly documented (the API docs literally contradict each other in places, while I couldn't even find a definitive guide to setting up a proxy and making it autoconfigure), making it difficult to know the correct approach and be able to test things on our side.
You can download the updates from the website, and subscribe to the New Releases area of the forum for notification of updates, as an alternative. The installers posted on the website and here at the forum are exactly the same ones the update checker downloads.
Just FYI, I found GitHub - ecovaci/winfoom: Winfoom is an HTTP(s) proxy server facade that allows applications to authenticate through the proxy without having to deal with the actual handshake. to be a valuable tool for proxy testing. Maybe it's of use for you, too.
Thanks, I had not found that before and it looks useful!
Still leaves the question of how to create a test environment to see if things work and debug them if they don't. (Otherwise, we'd have to keep going back & forth with test versions for other people to try, which could take a lot of people's time.)
I was surprised by how little information I could find on setting up a typical enterprise HTTPS proxy environment. I presume the knowledge is out there but maybe it's all specific to enterprise proxy hardware/software solutions which we don't have access to. If you know of anything, please let us know!
It's not exactly on that point, but I found Pros and cons of using a Http proxy v/s https proxy? - Stack Overflow valuable on the general topic, and also the linked c# - Transparent Proxy giving SSL error when accessing via https - Stack Overflow.