I did a fresh install of WP 2.5 when I was receiving all the errors and such. I could not even log into the Zen Cart admin -- and wordpress was in a sub folder, not the root folder w/ Zen Cart. So, really not sure why it is working for you but didn't for me. Unfortunately, it was very important that I uninstall it immediately for obvious reasons. Maybe I will try again with a fresh install of Zen Cart and WP 2.5 -- and see how that goes.
I wish the guy who created this mod was still supporting it. I haven't seen any activity from him in quite some time.
Thanks for letting me know it worked for you! At least I have some hope and will try again.