Hi,
Could you please describe us the upgrade steps you have made? What was the initial
CMS version?
After each upgrade - have you visited your site to check if it is working? Right now, it is hard to isolate where the problem occured and more important thing is that you must start the site - there are some thing being imported on the first start as well as some code executed when the application is started.
I would like to recommend to perform the upgrade again and after each upgrade run the site and check for errors, try to login at least.
Best Regards,
Juraj Ondrus