nagios check_snmp does not work but snmpget does

check_snmp of nagios uses version 1 of SNMP automatically, to force version 2c for the devices that do not support it add a -P 2c to the switches.

Also to check what snmpget is executed by the check_snmp simply run it with -v switch

snmpget works but nagios check_snmp does not

run your check_snmp with -v so it displays what exact snmpget it is calling