3.4.3 hangs at startup after Mountain Lion upgrade
I finally upgraded my iMac (iMac7,1 Core 2 Duo) from Snow Leopard to Mountain Lion and Aperture from 3.2.2 to 3.4.3. When I start Aperture, all I get is its menu bar with all menu actions grayed out. Activity monitor shows it's using 100% of one core. The only way to stop it is Force Quit.
I removed Aperture preferences and deleted and re-installed Aperture from the App Store. Makes no difference if I start Aperture while pressing Option or Option-Command; I get no pop-up asking me which library to use or showing repair/rebuild options. I re-installed Mountain Lion from the App Store. I deleted my Aperture library (after backing it up). I found and deleted every file on the system with "Aperture" in the name. I ran Repair Disk Permissions in Disk Utility. I started in single user mode and ran fsck (no problems reported). Nothing makes any difference; all I get is the menu bar and a pegged CPU.
I have determined that it's something in my account. I created a new account and copied my Aperture library to it. Aperture started up normally and upgraded my library to 3.4; it runs fine in a different account on the same machine.
I don't want to nuke my user account and make a new one, but it looks like that's the only thing left to try if I want to run Aperture in the same account where I read email, surf the web, edit documents, etc.
Any ideas what could be causing Aperture to hang when started from my account but run fine in another account after upgrading to Mountain Lion and Aperture 3.4.3?