Rights required to change expertise scoring
You may want to ensure that the account used to run the Social Sites Managed Service Application has write rights to the SharePoint configuration database.
Also, the person performing the recalculation of Expertise scores must be a farm administrator. Without these rights, the Recalculate functionality for the Expertise feature cannot work.
For further details on the Recalculate functionality, see Recalculate every time you change the weights in Setting up and administering the Expertise feature.