Hi,
Yep, that is because you need to do few things ... some changes are and will be made in the future by metasploit devs, but you can do this before that.
1. Start postgreql from Menu>Services>PostgreSQL>use restart option
2. Run msfconsole (maybe just before that run msfupdate for any case you didn't run upgrade for long time)
3. Inside msfconsole type db_connect
4. Check if connected in same window type db_status
5. Run Armitage
This is how i pull over this "error".
Cheers!