Sometimes Word application or other applications in Office quit unexpectedly or an error causes add-ins to stop working, it is disabled. Please follow the steps below to enbale it.
Step 1: Go to menu File -> Options
Step 2: On window "Word Options", click "Add-ins" on the left panel.
Look to the right, click combo box "Manage:" select "Disabled Items"
Step 3: On window "Disabled Items", select items that you want to enable them, click button "Enable", click "Ok" to complete.
Now you close Word and open it again.
Example design task pane in Word by activex control BSAC.ocx