SNMP Queries with Error "No such instance currently exists a this OID":
[root@web ~]# username -c public_1 -v 2c 10.158.151.111 1.3.6.1.4.1.5951.4.1.1.54.1.4 SNMPv2-SMI::enterprises.5951.4.1.1.54.1.4 = No Such Instance currently exists at this OID
Upgrade to NetScaler 12.0 build 60.x or 12.1-50.28 and later.