Ok thank you very much I appreciate the support and timely response. 
Hello,
Won’t install here either
Plain configuration 64 bit W8.1, nothing special and everything runs smoothly. Never happened before,
Gerard
Same exact issue here too. Just activated my trial version last night…
Best to avoid this then yes?
Really a big shame that Steinberg does not provide customers with DVD’s any more when they want.
I had to buy the Cubase Pro 8.5 upgrade download because Steinberg does not sell hardcopy updates anymore to his customers. Shame! I am Cubase user since version 1.0. Got all the boxes and disks/CD-ROM’s/DVD-ROM’s. But now I must do with a download… How can I put the 8.5 DVD in the computer when you don’t deliver them to updating customers? I had to re-install Cubase Pro 8.5 from the download now. In my opinion because a buggy installer from Steinberg this time. And I WAS so enthousiast of your installers lately. Untill the The Grand 3 online installer then. That one is even worse than this one. SHAME Steinberg…
I truly hope it is not going to be the same with Cubase 9 in about 9-10 months! Get us hard-copies again! And better installers!
I solved it here by just clicking “Repair” with the original Cubase85_64bit.msi installer, then proceeding with the 8.5.15 update. It shouldn’t be this hard, should it?
But it is far from how it is supposed to be!
I am happy for the solution but I think Steinbergs servers are getting whacked hard. I might be wrong but I don’t believe I ever had the the full Cubase 8.5 installer I bought the update when it came out and I don’t think it was 9.4 gigs.IS this possible?
So you’ve got to download the full 8.5 installer? All 9.4gb of it?
Steinberg need to fix the installer. I’ve been running ccleaner and its reg cleaner for years and never had this issue.
Hi I have managed to get the update to load by deleting 8.5 then going to MySteinberg and downloaded 8.5 again but I was in tears when I saw how long it takes to download 9.4 Gigabytes. Then I loaded 8.5.15 successfully and I was out of my comfort zone as I explained in my earlier post, still it wasn’t the end of the world and I’m back happy again so thanks everybody. I am laughing most probably have messed something else up Regards Colin
Good news Collin! My download just finished. I hope to be back in the game with the update soon. - Cheers from Canada … the other side of the pond.
QUICK FIX;
Run the 8.5 installer update(876mb),extract,find Cubase85_64bit,right click,hit repair,after its finished install the latest update.It works,its the fastest solution.
AND PLEASE STEINBERG ADD MONO/STEREO OPTIONS WITH RIP IN NEXT UPDATE.
+1
Hmmm,… I’m not even going to bother updating after reading all these issue on this thread.
Yes, Steinberg needs to fix the installer, rather have us waste our time to install an update that is a fix to a fix , what a mess. 
Hi all,
I just downloaded, and ran the 8.5 installer, which automatically downloaded the 8.5.15 update.
The entire update (8.5 & 8.5.15) still failed???
This seems a bit silly to me because, even though I am not a computer wiz kid, it doesn’t make sense that I have to run the 8.5 update (which I had already installed) to get the 8.5.15 update.
Having never had this issue before, I would guess that someone dropped the ball at Steinberg and I would like to think the problem will be rectified very, very soon!!!
To put it simply, we have all paid for the top of the range programme and yet we cant update it, and that smells of bad customer relations!!!
Would someone please let us know when the issue has been fixed because I and the other CBP 8.5 users are not happy!!
Jim B
Sorry to hear it from you guys but I’ve downloaded 8.5.15 and installed it with no troubles. Win 8.1x64 Cubase Pro x64. It’s not a dedicated computer, all programs I need in my life are installed on this system including some 3D shooters 
Hope you’ll sort your issues out soon.
Best.
Same problem here. Now trying to download the full 8.5 download so I can start from scratch.
But, it’s 9GB - will have to wait until tomorrow.
Or, skip this update. 
NO.
Dont download the 9gb file,download ONLY the 8.5 update(875mb).
Run,extract it and then run Cubase85_64bit with right click,hit repair and after its finished run the latest update.
It should work.
I’m guessing that people who have issues with the installation of 8.5.15 have, at some point, had their registries altered. This might be because of the use of registry cleaners, it might be a Windows update patch installation, another program etc.
What it isn’t, I don’t think, is an issue with the Steinberg installer. Why should it be? If the Steinberg installation registry entries are OK, then there won’t be an issue. If they’ve been altered, deleted etc, then problems will happen.
I had to re-install 8.5 when 8.5.10 came out. It wouldn’t install 8.5.10. My bad. I’d run a registry cleaner, not checked the findings and just clicked delete. Embarrassing? yes, lesson learnt? yes.
I know it’s frustrating, but user errors, mistakes, misunderstandings account for the majority of problems down the line. I’ve done my share of them, believe me.
Thank you !
It worked like a charm.