Any extension that interacts with users in any way, shop or form, requires the #__users table. It sounds like you have migrated the EasyBlog data, but forgot to migrate the data from the #__users table on the old site to the new site.
This would explain why the user ID doesn't exist and the error you're receiving.
You need to export and import the following tables:
#__users#__user_usergroup_map#__usergroups(only if you have custom usergroups)