I was having the same problem with with the YARRP database error message. I have corrected the problem on my sites and this may help others who are struggling with the same error.
1. Are you using an alternate prefix in your MySQL database (something other than wp_?)
2. If so, check to see if these two files: (prefix)_yarrp_keyword_Cache
and (prefix)_yarrp_related_Cache have different file prefixes (example: cg_yarrp_keyword_cache and wp_yarrp_related_cache) in MySQL.
In my case, the Keyword Cache had my custom prefix and the Related Cache had the wp_ prefix.
I renamed the Related Cache file (changed the wp_ prefix to match my Keyword Cache prefix and all is working fine.
I hope this helps someone out there. I’m just glad to have the “GREAT” tool working on all my sites.
Mike Gerow
DailyKnowledgeTree.com
