Hey Bob.
I am really sorry that delay of this reply,
To fix this, you have to find this user which discussion post he created before then change to another user existing id.
To permanently fix this, you have to install this user plugin (plg_easydiscuss_users.zip) and set `Owner for orphaned items` from bacekend > Easydiscuss > settings > maintenance
What this option task is actually specify your new ownership for those orphan items such as posts, tags, comments and etc upon user removal. Insert User ID here to set the new owner for those orphan items. Default is 62, which is an admin account when you first install Joomla.
Hope this help.