This has always happened pretty much with all versions of Cubase, but it really got worse with 7.0 and 7.5 and it´s still not better at all with 8.0.
Pretty much every fift time (estimate) I close a project, Cubase crashes. I get at least two crashes per day with Cubase. Many times more. This means in a year I get probably at least 1000 crashes. 
What is the main reason why Cubase crashes when closing a project?
Mac Pro Early 2014 12-core
OS X 10.9.5
Cubase 8.0
Probably your 3rd party plugins is causing this.
If you load a blank project with no plugins and close Cubase…does it crash still?
And to me the same problem.Im want to get out of the project cubase 7.5 after a stint cubase break down.
What the problem? 
Nope, but neither does the projects with 3rd party plugins…
…like 4/5 of the time. 
And this has seriously started happening a lot more often since the launch of Cubase 7.0.
For me
I had this problem before and it was Altiverb 7.2.3 causing this. I updated To 7.2.4 and no more crash on quit or close.
If you don’t use altiverb try isolate the problematic plugin.
I’v had this problem since 7.0. 1/4 of the time Cubase hangs on closing. Stopping the application in TaskManager doesn’t help, it only moves de program to a background task. I have to power off/power on, otherwise my UR44 interface will remain stuck too.
I’ve tried a lot of things:
Using the latest drivers, naturally.
But still… The SAME project sometimes hangs on exit en sometimes doesn’t. I’m out of ideas!
Melodyne will crash cubase on exit. Workaround is close the project before quitting the software (Mac version)
Best,
I had similar problems with 7.0, it stopped in 7.5 and in 8.0 no problems closing the program.
Big difference is that I had loaden many plugins (including 32 bit ones) with the 7.0 setup. After installing C7.5 I removed all freeware and try stuff, the problem vanished 
If Cubase doesn’t crash 100% of the time without plugins loaded then the lead suspect is one of your plugins is causing this…and most likely a 3rd party plugin.
Of course it´s the “3rd party plugins fault”, what else could it be. Certainly not Cubase!
Oldest excuse in the book!
I pretty much use only Waves, UAD, DMG Audio, Slate Digital (not VCC or FG-X) plugins and PLAY and Kontakt VSTis.
But what is the reason of the crash? Even if it´s caused by a 3rd party plugin? Cubase can´t handle 3rd party plugins?
When talking about 3rd party plugs, you have to keep in mind that with 30 vendors there are 30 ways to code things.
Plugin system are by default weak systems, but very flexible. You’re bound to stability of the weakest link, in this case we can say with confidence that the plugins are the weakest link (beside the bugs which are present in every version of cubase).
Bottomline, you can’t blame steinberg alone, the other have their part also!!!
Okay so the solution is not to use 3rd party plugins? Then Cubase is ok and does not crash?
Maybe Cubase just can´t handle 3rd party plugins like other DAWs can?
Also I must add, that before 7.0 I used much more variety of 3rd party plugins and the crashes happened less often. Now I only use few trusted plugins from the most respected plugin companies.
I used to have this problem on 7, not 7.5 and not 8. Wasn’t related to plug-ins. It happened on Windows every time I tried to quit Cubase using the standard Windows ‘x’ button on the top right of the main Cubase window. Didn’t happen when I went File>Quit.
I had the problem some time ago, it turned out to be a midi driver for an old keyboard. Does Not hurt to have a look if there are updates to the drivers of the hardware you use.
Licensetokill: can you please compress the crash dumps in an archive and send them via PM to me? They are located in Documents → Steinberg → Crash Dumps. Could also be a driver or another component that does not respond to the closing message of Cubase, so I’d check the dumps before saying it’s a plug-in.
Thank you.
[Edit: was writing when peakea posted, he added more details to what I meant for “a driver or another component”]
I have this on every close of a project.
It maybe is console one on my system. They had that problem in 7.5 Then softube fixed it. With 8 its there again.
No, the solution is first to find the offending plugin or device and then find out if an update is offered by the vendor which might resolve your problem. Why is that not an acceptable and understandable scenario??
How the hell can I find such a plugin when the crashes are random?
Actually I already thought I found the plugin. I had two instances of Softube´s TLA-100A in one of my projects and that project started crashing EVERYTIME I closed it. I removed the Softube plugins, saved the project and voila, no more crashes! Aaaaaah it was the freaking Softube plugins that caused the crashes! I was 100% sure it was the Softube plugins. Weeeell… not quite! Things are not what they seem.
Then I did a test. I opened the same project and put the same instances of Softube plugins back with the exact same settings, saved again and closed the project. Didn´t crash anymore! Weird, right? Why does it not crash anymore with the Softube plugins back in the project?
Then I removed the Softube plugins again just to be safe. But then later the crashes are happening again and totally random!
So in my mind I can only blame Cubase´s unstability and it´s ability to handle 3rd party plugins which is absolutely horrible! The plugins are not to blame here. Just Steinberg, VST format and Cubase!
Maybe it´s time to go AAX or AU soon, because it seems that VST is a bad format and Cubase just can´t handle it.
Unfortunately your assertion that Cubase doesn’t handle 3rd party plugins is preposterous when the majority of us are using many 3rd party plugins without them crashing our systems! Logic dictates that there’s a problem with your setup. Cubase is not unstable, but your computer might be. Open a support ticket with Steinberg. Maybe they can help troubleshoot your computer. I’d also check to make sure all your plugins and device drivers are current including OS updates. You should list your hardware. Maybe it is your Sound device driver that is causing the problem.
But why closes on project in 7.5 just fine and the same project crashes everytime on closing in 8 ?