[SOLVED] [Checkout] Upgrade from .42 to .43 broke cart display

Gallery URL = http://www.canigetacopy.com/gallery2/main.php
Gallery version = 2.3 core 1.3.0
API = Core 7.54, Module 3.9, Theme 2.6, Embed 1.5
PHP version = 5.2.5 isapi
Webserver = Microsoft-IIS/6.0
Database = ado_mssql Microsoft SQL Server 2005 - 9.00.4053.00 (Intel X86) May 26 2009 14:24:20 Copyright (c) 1988-2005 Microsoft Corporation Standard Edition on Windows NT 5.2 (Build 3790: Service Pack 2), lock.system=database
Toolkits = Exif, LinkItemToolkit, Thumbnail, NetPBM, Gd, ImageMagick, jpegtran
Acceleration = partial/900, none/900
Operating system = Windows NT EPWS1 5.2 build 3790
Default theme = carbon
gettext = enabled
Locale = en_US
Browser = Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0)
Rows in GalleryAccessMap table = 2181
Rows in GalleryAccessSubscriberMap table = 35113
Rows in GalleryUser table = 65
Rows in GalleryItem table = 35099
Rows in GalleryAlbumItem table = 466
Rows in GalleryCacheMap table = 102964

I was running along fat and happy with 0.42 and decided to upgrade to 0.43. After I did, all Checkout display pages returned HTTP 500 errors. I tried everything I could to revert to 0.42, including reverting to a backup of an earlier Gallery2 install and restoring a previous database backup and no dice. So I did a complete uninstall of Checkout and all its add-on modules, deleted the directories, and reinstalled & configured just Checkout. Now I can open Checkout Config and Checkout Orders, and I can add things to the cart, but if I try to open the cart I still get HTTP 500. Same when I try to open any of my current sessions.

Here's my URL for viewing the cart:
http://www.canigetacopy.com/gallery2/main.php?g2_view=checkout.Select&g2_return=%2Fgallery2%2Fmain.php%3Fg2_view%3Dcore.SiteAdmin%26g2_subView%3Dcheckout.AdminSessions

Here's my URL for viewing a current session:
http://www.canigetacopy.com/gallery2/main.php?g2_view=core.SiteAdmin&g2_subView=checkout.AdminSession&g2_sessId=b626d5264ee3bb46a35e5c37020cc677

The site's live, so you're welcome to try to add something to the cart yourself.

I vaguely remember that there is a PHP.ini option to make it give you verbose HTTP 500 errors, but things have worked so well for so long I can't remember it now, and I'm not even sure that would be helpful.

I really need a working cart and I can't try Gallery3 because I'm a Microsoft monkey.

Thank you for any direction you can provide.

Thanks for the quick reply. I output the debug log to a file. Unfortunately, the debugger doesn't seem to register clicks to the problem links.
The first attached file is just opening the homepage and clicking on the cart link.
The second attached file continues into site admin, checkout orders, and into current sessions. Again, once a session was clicked, instantly HTTP 500 with no debug record.

Earlier, I also tried turning on PHP error logging and got nothing.
I also tried to get IIS to generate a more verbose HTTP 500 error message, and still nada.

So, I've turned on Buffered debugging in case you'd like to go to the site yourself.

Many thanks

WOWZA!!! I have spent hours and days trying to fix, reinstall, upgrade, and nothing. And I could have spent another week and I wouldn't have found what you found. Even more, you found it within minutes of my asking.

You truly are a scholar and a gentleman. So I must ask one more thing, I know how to PayPal Contribute to Gallery, where can I PayPal Contribute to Checkout?

For now, thank you very much!