Ah, sorry I missed that you said you have tried to reinstall already. If you reinstalled with the latest download from your Spine license page, then it should not show that dialog anymore. I tested this again just now and it's working correctly.

Could it be that you aren't reinstalling the latest? If you are on Windows you should see Spine Launcher 3.8.81 in the title bar during installation:
 Loading Image

Also when you run Spine, your spine.log should start with:

Spine Launcher 3.8.81
Esoteric Software LLC (C) 2013-2020 | http://esotericsoftware.com
...

You can find your spine.log here:
Windows: <user home folder>\Spine\spine.log
Mac: <user home folder>/Library/Application Support/Spine/spine.log
Linux: <user home folder>/.spine/spine.log

It's definitely not an ideal situation and I apologize for the trouble it causes. The problem is that older installers contain a certificate that will expire soon, on February 15, 2020. Everyone needs to reinstall Spine with the latest installer, else after that date the old Spine installations won't be able to reach the server. This certificate problem won't happen again in the future.

It is rare that we force Spine to be reinstalled like this. We won't need to do it again until version 4.0, for that you'll need a new installer because we will move to 64-bit. The upside is that then Spine will be able to make use of all the memory on your system, rather than just 1GB that 32-bit apps are limited to.

Tagging onto this thread for more information.

I ran into this same issue but I did reinstall the new version of Spine to get the error dialog go away and to be able to use the software once again. At this early point in my project, this is fine but I'm more concerned for the future. Towards the middle of the lifetime of our projects, we tend to 'lock down' the version of our animation and game engine software versions. This to help us with bug fixing for ship dates (and milestone deliveries) as well as to prevent bugs in general that can creep up with updates. In the future, will there be a way to 'lock' the version of Spine and/or prevent the force update?

Thanks for any updates in advance!

It is good you are wary of keeping the same version of the Spine editor, especially near a release. You can set a specific editor version to do that:
Settings - Spine User Guide: Version

The version of the Spine launcher is different. Any Spine launcher can always run all previous versions of the Spine editor. Usually when we update the launcher, it improves things but is optional. Occasionally we do an editor release that requires new functionality in the Spine launcher. When that happens the reinstall dialog is different

it only asks you to reinstall if you try to run the latest editor version, and it lets you choose an old editor version if you don't want to update the launcher at that time. This latest launcher update is different

it is mandatory because if you don't update then your old launcher has a bug (a certificate expiration) and will not be able to reach the server after February 15, 2020. That's not good because the only error you'd see is "the server cannot be reached". This is the first time we've ever had to do a mandatory launcher update, and hopefully the last time!

Ah, thanks for all the info Nate! This is a huge sigh of relief for me and my team. I understand the certificate issue but it just brought up future concerns.

i'm getting an error message saying that i cant update spine - because the server returned an invalid response? - anyone having this problem

We had a minor server hiccup this morning, but it's all taken care of now. Sorry about that!

I'm running into this issue.
I have Spine on 2 stations : my mac runs just fine but I had the server error on windows 7.

Tried to reinstall it, it seemed to work but as soon as I go offline it tries to reach spine server again...
I really need my windows laptop as this is my offline/travel computer

How can I fix this bug ?