It looks like you are missing the mibs. Either they aren't there (sudo apt-get install snmp-mibs-downloader) or /etc/snmp/snmp.conf is not set properly. I'd try the get and then take a look in snmp.conf to see if it sets mibdirs correctly or sets mibs incorrectly.
I did a quick web search and it looks like Ubuntu doesn't install the mibs so the above is necessary (cannot confirm as my linux box is Centos).