Hi Ipstenu,
Prior to deactivating all the plugins, which I did by reaming the plugin folder), I did add this line to both wp-config.php files on both of the sites.
define('WP_MEMORY_LIMIT', '96M');
It wasn't clear where I should add it so, in one wp-config.php file, it is above the database define statements and in the other it is just after those declarations.
How do I tell whether or not that setting is being used by WordPress?
After activating the new wp-config.php files, I moved the plugins from the renamed plugin folder to the newly created plugin folder one-by-one to see which one caused the failure.
The site that isn't running Shopperpress 4.3 allows me to use the phpbay plugin but not the amazon plugin.
The Shopperpress 4.3 themed site failed when I moved Akismet to the new plugin folder, at which point I tested changing the theme to TwentyTen. As I mentioned earlier, changing the theme to TwentyTen at the 2nd site made the "nice to have dashboard content" reappear but that site is meaningless without the cart layout so I reactivated Shopperpress.