Step 1: Grant read/write
Using SQL server management studio
expand the security tab, then the logins tab
open the properties for the AGS server account login (by default the username is "arcgis" and it could be a domain or local user), then click User mapping
in the top pane, select the db in question
now in the bottom pane check the boxes nect to datareader and datawriter roles
click ok
Step 2: Remove AGS account from sysadmin server role
Expand the security tab, expand the Server Roles tab
open the properties for the sysadmin role
select your AGS account user and click "remove"
Step 3: reboot the server.
I had our IT department do this for me.