Solution:
You must probably still have invalid paths or urls in your updated database, or might be replacing serialized data with unserialized data. There’s a really useful plugin for WP Db migration called WP Migrate Db. You should give it a try. If you do, don’t forget to replace both urls and paths:
URL Example:
//localhost/sites/yoursite/
with
//yoursite.com
Path Example:
C:\xampp\htdocs\yoursite
with
server/path/to/yoursite
This path is usually detected by WP Migrate Db.