As the message states, it seems your interface is dropping SNMP packets due to the input queue of that interface being full when those packets arrived.
You should use 'show snmp' to see how many packets have dropped.
Please see the following link for the Error Message Decoder for more info:
http://www.cisco.com/cgi-bin/Support/Errordecoder/index.cgi
(requires cco login which is free)