Aperture library suddenly won't open

Question

OK, I've been putting off updating to the latest version of Aperture (3.4.3) because I had a sort of premonition about something bad happening to my library. But I finally got around to doing the upgrade, having felt this version had been around long enough to be stable. Big mistake. It worked OK initially, but suddenly today won't open my library, no matter what I do.
When I launch Aperture, it opens a little window with a spinning marker in it and the message "Opening Aperture Library". This is normal prior to the main window opening, but usually I see it for no more than a second or so. Now, it's all I see; the main window never appears.
Oddly, Apertur's menu structure seems to work OK while this 'loading' window is open. I can, for example, open the Activity window. However, it contains no useful information to say what's going on; the entries are just blank in this window. Also, I can quit Aperture normally (whereupon it says 'updating previews' as usual).
I've tried all three of the database-reparing options that Aperture offers if you hold down Option-Command when starting: repair permissions, repair database, rebuild database. In all three cases, it goes through the repair process and then just reverts to showing the little 'opening library' window and nothing has improved.
The upgrade to version 3.4.3 apparently went OK the other day, and I've opened and quit the software a few times since I upgraded it, and I thought everything was fine. The one thing that wasn't quite right (and I wonder if this has somethnig to do with my problem now) was Photo Stream. It didn't seem to be working properly. If I clicked the Photo Stream entry in the list at the left of the window, what I saw was just the 'welcome' message with buttons below it to sign in or turn off the service ("No, thanks" button). I didn't see any actual Photo Stream content. In this window, however, it *did* say that I was signed in with my usual Apple ID, so it wasn't very clear to me whether it was OK or not.
There's a photo I took on my iPhone which I was expecting Aperture 3.4.3 to download from Photo Stream, but it never did. I.e. just one shot that failed to download; all the previous ones had been downloaded by my previous version of Aperture. I couldn't see why the missing picture was failing to download, so I tried turning Photo Stream off and on again from within Aperture. I'm really not sure whether this worked or not; there didn't seem to be any meaningful feedback from the software.
Anyway, after having tried to launch Aperture today (and failed), I checked System Preferences and found that Photo Stream was turned off. So I turned it on again. Unfortunately it makes no difference: Aperture still won't load its library at all now.
I have tried all of following:
1. Rebooting my Mac
2. Verifying the disk contaning my Aperture library (it was fine)
3. All three of Aperture's database-repair options
4. Turning Photo Stream on in System Preferences
...and nothing makes any difference. Aperture simply will not open my library but just sits there, twiddling its spinner.
NB My library still appears to be OK, in that I can access its contents from other software successfully using the media browser.
What I haven't yet attempted is to create a blank new library and import my existing library into it. Failing any better ideas I'll try that next, but it's going to be a big operation that will take a lot of time and disk space, so I'd like to see if there are any better things to try first.
I must say I'm very disappointed that Aperture can apparently break so easily. I haven't lost any actual pictures because I'm paranoid and keep a separate copy of all my shots just in the Finder, external to any management software. But I've lost access to lots of photo books I've created over the years and various other resources, not to mention all the editing work I've done on thousands of shots within Aperture (which I haven't retained separately).
This is supposed to be professional level software. How can it seriously (a) break this easily and (b) not be able to retrieve itself via its database repair options?I'm very disappointed.

Answer 1

Thanks for that very helpful reply. I've followed your instructions and done some further digging too.
To answer your three points, first of all:
1. No, I haven't imported any images since upgrading my Aperture library for version 4.3.4; I did move photos between projects a couple of times, but mostly I just checked that everything appeared OK after the upgrade and tried to work out why PhotoStream didn't seem to be working properly.
2. I've attempted to create a new Aperture library. This didn't work! A library gets created on disk, but attempting to open it produces the same endless spinner as the main library.
3. I switched to a spare user account (a blank one called 'test', just as the system created it) and tried to launch Aperture and create a new library there. Same result: library is created but won't load in.
This is very strange, because I'm not aware of having changed anything substantial on my system recently. No new software that installed anything as a login item, system service or background process etc. that I'm aware of. (I'm actually quite wary of such software, and don't have much of it on my system.) The only substantial thing that I know has changed since I last successfully launched Aperture is the year, to 2013! And I hardly think that's the cause...!
I'm wondering if Aperture itself has become corrupted somehow, and whether I should trash it and reinstall it. But that's rather a pain because I've got the DVD version, not the one from the Mac App Store. Besides, I'm not sure what remnants it leaves on the system (sandbox files etc.).
I've verified my startup disk, on which Aperture resides, and repaired permissions, and no error was reported (nor did many permissions need to be fixed).
Now, the only other possible explanation I can come up with is that startup is being prevented by a misbehaving PhotoStream process, as I've just discovered that I'm having endless crashes from PhotoStreamAgent, as reported in Console. I'm getting the same series of messages popping up every few seconds:
01/01/2013 21:58:51.649 xpcd[4676]: PhotoStreamAgent[5540]: registration request failed: (0x11, 0x0) The file “com.apple.iLifeAssetManagement.agent.plist” couldn’t be saved in the folder “Preferences” because a file with the same name already exists.
01/01/2013 21:58:52.431 com.apple.launchd.peruser.501[473]: (com.apple.photostream-agent[5540]) Job appears to have crashed: Illegal instruction: 4
01/01/2013 21:58:52.431 com.apple.launchd.peruser.501[473]: (com.apple.photostream-agent) Throttling respawn: Will start in 10 seconds
01/01/2013 21:58:52.615 ReportCrash[5531]: Saved crash report for PhotoStreamAgent[5540] version 2.7 (40.34) to /Users/rghallas/Library/Logs/DiagnosticReports/PhotoStreamAgent_2013-01-01-2158 52_Richard-Hallass-Mac-Pro.crash
01/01/2013 21:58:52.620 ReportCrash[5531]: Removing excessive log: file://localhost/Users/rghallas/Library/Logs/DiagnosticReports/PhotoStreamAgent _2013-01-01-215516_Richard-Hallass-Mac-Pro.crash
This is just repeating every 10 seconds, as suggested by the 'Will start in 10 seconds' message. Starts; crashes; loop.
Now, I've searched for a file called "com.apple.iLifeAssetManagement.agent.plist" and have found three instances: one each in the following places:
Aperture:
/Users/rghallas/Library/Containers/com.apple.Aperture/Data/Library/Preferences/c om.apple.iLifeAssetManagement.agent.plist
PhotoStream Agent:
/Users/rghallas/Library/Containers/com.apple.photostream-agent/Data/Library/Pref erences/com.apple.iLifeAssetManagement.agent.plist
iPhoto:
/Users/rghallas/Library/Containers/com.apple.iPhoto/Data/Library/Preferences/com .apple.iLifeAssetManagement.agent.plist
In all three cases, the file appears to be an alias that points to itself (i.e. original path is the same as the alias's path in each case). That seems weird but I hope it's right, given that it applies to all three (and the files alongside these plists in the folders in which they reside).
Anyway, the logs unfortunately don't make it clear exactly *which* Preferences folder is being referred to, and hence which com.apple.iLifeAssetManagement.agent.plist file is causing a problem. I imagine it's the one associated with PhotoStream Agent, since it's the Agent that's producing the ongoing crash reports. But either way I don't know what to do about it. I suppose I could try trashing this particular plist file, but I'm reluctant to do so as I don't want to break anything further.
NB Aperture itself doesn't appear to output any log messages to say what's happening while it's failing to load its library.