1146 - Table 'mybb.mybb_reportedposts' doesn't exist
I have looked ever were though mybb and the internet and I looked for plugins that do reporting and it still does not work.
As the upgrade guide recommends:
http://docs.mybb.com/1.8/install/upgrade/ - Preparing for your Upgrade Wrote:You must deactivate (or disable) all of your plugins. This is because it is likely they will need to be updated to work on the new version and can cause problems if they are left active.
You didn't post the whole SQL query from the error, so we have no idea which plugin it may be either. It may be anything connected with reports/moderation/posts.
O Sorry, I have just fully reinstalled to fix this problem.