Ran into this exception today when I tried to Export Ranks in the ACP. My core_member_ranks table doesn't have a 'posts' column. I am using a DEV install and I think I am on the February release (haven't upgraded to March yet).

Are you using the latest version?

This was fixed in 4.6.10

Sorry, I'm using 4.6.9... Should have checked that first before reporting...