You must enable chat services in order to create chat sessions or receive chat invitations.
Turn Off Chat Services...
Disallow chat invitations
To temporarily disable chat invitations while retaining the ability to create and participate in chat sessions, choose Window ▶ Chat Settings and uncheck Accept new invitations:
- Leave chat services activated when not accepting chat invitations to make a record of chat invitations that were refused.
Disallow chat services
To turn off chat services completely, choose and uncheck Allow Chat Services on the Services tab:

- Turning off chat services prevents the "ChatServices" kernel, which manages chat connections, from starting.