Hello, I've been following this post and the Microsoft thread as Albertico mentioned 10 days ago at the top of this thread. I believe I have some other useful symptoms that can be added.
Before I mention those symptoms, I would like to mention that I saw there is a new Opera update version "51.0.2830.40". So I redownloaded Opera and it is doing the same thing as the last update. Which is that it loads up tabs automatically at startup. I again uninstalled Opera and the other error message still appears at startup again. So if the new version that is out was suppose to be the fix, it did not fix the issue. I am looking forward to it being fixed since I would like to use Opera as my default browser again.
Anyway, back to the added symptoms. I have a unique situation since Opera is working on my Windows 10 desktop (with carbonite) just fine. However, on my Windows 7 work desktop (also has carbonite), that is where Opera is not working.
Both desktops has/had Opera as default browser (currently uninstalled on Windows 7 until there is a fix).
Opera on my windows 7 after it was manually updated it had began auto loading tabs at startup, as others have stated. What I have not seen others mention is that these tabs do not ever load. I've tried closing all of them down to one tab and typing google.com and that eventually loads up but doesn't let me click anything to go to the next page. For example I can't click sign in to my email.
Something else I noticed on the windows 7 Opera in and out of fiddling with it when the error first came up and then again in and out of installing it seeing it its fixed yet.. I have some preset tabs to auto open, 4 to be exact. So when my Opera opens it opens those 4 plus 3 more and 1 speed dial tab. All of which never load as mentioned above. For the sake of less tabs opening I tried to set new tabs to just load google.com at opera startup. When trying to do this, the set tab section when I click to use current tabs, it is blank. However, it did manage to select to open just google.com.
Lastly, because Opera seemed like it was trying to load and partially got to google.com even though I couldn't click around. I figured I'd try clearing the cache and browser history just in case it is recalling loading bad links. So when I tried this, that also would not process my request. It would allow me to click to clear the cache and browser history but it would just get stuck in an endless loading.
I think that sums up any input I can add for now that others have not yet mentioned. Aside from maybe digging deeper into comparing what my windows 10 desktop has or doesn't have compared to my windows 7. I would need to know what I should be looking for if that is the case. I don't really know to much about registry issues so I can't contribute there. But I can say that my windows 10 has Microsoft edge and windows 7 has internet explorer. I know I've seen comments saying carbonite runs on a component of Internet Explorer, I assume that same/similar component is in Edge? or maybe it is not which is why my windows 10 is running fine. Others mentioned they are having this issue on a windows 10 so im not sure where I got lucky in that regard but my windows 10 is running Opera version 51.0.2830.40 smoothly as default browser.