Q: Are you trying to open Cubase 12 via the ‘Run as administrator’ option? If you are, this might explain your problems.
See link: When I open C12 and select 'Run as administrator' - #3 by Riggs
Soultion: Restart your DAW and don’t use this run option. My DAW is Win10 latest version. All the best.
I have always ran Cubase as administrator, for years. I have never had any trouble with it. It has solved more issue that it has ever caused, because it’s never caused an issue.
When did you say you were leaving?
So many people say this cannot happen. Yet so many say this is happening to them. 
That’s the main reason I’m waiting to update to C12 Pro now.
And there are many others none of this is happening to, so to blame it solely on Cubase is a bit false as some us are getting on just fine and can go back and forth between 11 and 12 with absolutely no issues…
That’s been my experience. Working in C12 mainly though. In the time since the update very little that might be untoward has happened. I have had a couple crashes for which I’ve sent in bug reports. When a crash does happen I hit the button to send it to Steinberg.
The annoying crash I dealt with was Score Editor: Rhythmic Notation + Multi Rests = Crash. I’ve been made to understand that it will be fixed in the next update. In the meantime I use a workaround.
People who are working happily in the sequencer are much less likely to go to the trouble of coming to the forum to say how smooth things are going, so we are seeing quite a bias. Nothing new to that, but worth noting.
Highlights the question, IMO, how many users with problems are enough to say the release was premature and not successful? Or, how many very experienced users, not new rookie users, does it take?
When I see so many pros of many years experience (people who make their living using Cubase, who are used to routinely troubleshooting to keep their business running) posting that they can’t use this or that released version … knowledge that many users don’t have those problems isn’t all that reassuring, at least to me.
The most astonishing part of this thread is there is only one mention of a back-up system on what must be a business critical system to warrant this much distress over a software upgrade.
Given how little even an external hard disk and free imaging software cost if your business depends on it - make a backup before updating anything. Indeed make a regaulr backup anyway because of auto updates, ransomware, viruses, power outages…
Well, that’s a matter of opinion. If you mean for the manufacturer to say so, it seems doubtful any company would actually say that. But what Steinberg are doing is working on solving the problems that exist.
In regard to
I’m not sure that one can presume that each assertion of being professional is entirely accurate.
I only know the pros that I know personally – studio owners I’ve done sessions for/with as a musician over the the past 30 years, and the people I have gotten to know well (professionally speaking) online who are Cubase and Nuendo users.
I’ve observed among them, without exception, and I mean that in the literal sense, a new version of software is either tested on a non-production machine, or they wait for several releases before even trying. There’s too much at stake to risk problems during a session. Some people actually freeze their system, and never update once their setup has become dependable. So one might walk into a studio and see a cart with an old Windows XP running old software.
In regard to C11 not working due to a C12 install, please post links to these posts. I’ve seen this one, here the person seems to be having multiple problems in the system, and I seem to recall one other, but I don’t read every. single. post. that’s made.
In no special order …
No links posted here, sorry, but there’s a search function you know! 
I would, but don’t have the bandwidth/hence motivation to do so. I may remember/zero in on those posts more than you because they may be much more relevant to me (single machine i can’t afford to lose access to Cubase on). Anyway - I notice them.
[quote=“steve, post:63, topic:781079”]
But what Steinberg are doing is working on solving the problems that exist.
[/quote] I think it’s great they’re doing that. It would have been almost infinitely better if they’d done more of that before release, IMO.
Agreed, 100%. Even I, a happy weekend warrior whose Cubase use doesn’t pay the bills, knows to not mess up my work computer like that! But my impression is that some of the pros are venting here because they feel jerked around, not necessarily because they’re studio got bricked.
Here’s a totally OT thing your use of the word “literal” made me think of:
Did you know one of the definitions of the word literally is “not literally”?
Literally!
Wow. My head literally exploded when I learned that. But I meant literally in the literal sense. Not literally. 
You betcha. I do a daily disk clone, Windows File History, and an “offsite” backup.
What programs do you use for daily disc clone?
You clone the entire disc, things like c drive and os included?
Thanks!
Just to signal-boost this point - if you’re in any way depending on a computer system for work that’s in any way critical for your (financial or mental) well-being, then you will want a non-production machine that you test even the tiniest of upgrades on to make sure they work with your specific use cases before changing anything on your production system.
Or an alternate boot partition or boot drive. Which is much much less than a whole new machine.
Good point! The only (slight) upside is that if you have a non-production machine, you can use that as a spare, to hot-swap it in for production duties if your production machine goes down hard 
Or boot from a different drive. I mean if you want absolute redundancy then buy everything twice, but just another boot drive will get it most of the time unless it’s hardware.
So am I the only one who just downloaded the demo of C12 so I could see how it was without overcommitting?
I use macrium reflect for disk imaging myself.