I have distributed monitoring that using proxies for check devices on client-side.

Some of my proxies generates alot of errors:
1857:20141028:105659.890 SNMP agent item "IfHCOutOctets[FastEthernet0/21]" on host "rostovdon-1-sw1" failed: first network error, wait for 15 seconds
1799:20141028:105705.803 SNMP agent item "ifHCInOctets[FastEthernet0/20]" on host "izjevsk-1-sw1" failed: first network error, wait for 15 seconds
2502:20141028:105708.190 resuming SNMP agent checks on host "volgograd-1-sw1": connection restored
1910:20141028:105708.847 SNMP agent item "locIfInRunts[Vlan100]" on host "samara-1-sw1" failed: first network error, wait for 15 seconds
2266:20141028:105709.161 SNMP agent item "locIfCollisions[FastEthernet0/32]" on host "ho-1-sw2" failed: first network error, wait for 15 seconds
1765:20141028:105711.973 SNMP agent item "locIfInIgnored[GigabitEthernet0/3]" on host "ho-1-sw3" failed: first network error, wait for 15 seconds
2502:20141028:105714.215 resuming SNMP agent checks on host "rostovdon-1-sw1": connection restored
1706:20141028:105715.072 SNMP agent item "IfHCOutOctets[FastEthernet0/43]" on host "ho-1-sw4" failed: first network error, wait for 15 seconds
2348:20141028:105718.883 SNMP agent item "ifAdminStatus[FastEthernet0/18]" on host "lipeck-1-sw1" failed: first network error, wait for 15 seconds
1705:20141028:105719.233 SNMP agent item "locIfInRunts[GigabitEthernet2/0/6]" on host "n.novgorod-cc-c3750" failed: first network error, wait for 15 seconds
2502:20141028:105720.238 resuming SNMP agent checks on host "izjevsk-1-sw1": connection restored
1639:20141028:105721.030 SNMP agent item "locIfInCRC[FastEthernet0/20]" on host "n.novgorod-cc-sw1" failed: first network error, wait for 15 seconds
2502:20141028:105723.339 resuming SNMP agent checks on host "samara-1-sw1": connection restored
1760:20141028:105723.698 SNMP agent item "ifHCInOctets[Vlan20]" on host "stavropol-1-sw1" failed: first network error, wait for 15 seconds
2502:20141028:105724.348 resuming SNMP agent checks on host "ho-1-sw2": connection restored
2425:20141028:105725.493 SNMP agent item "ifInErrors[FastEthernet0/12]" on host "n.novgorod-cc-sw3" failed: first network error, wait for 15 seconds
2502:20141028:105726.356 resuming SNMP agent checks on host "ho-1-sw3": connection restored
1915:20141028:105727.808 SNMP agent item "ifOutErrors[Vlan1]" on host "n.novgorod-cc-sw4" failed: first network error, wait for 15 seconds
1999:20141028:105728.901 SNMP agent item "locIfInFrame[FastEthernet0/2]" on host "tula-1-sw1" failed: first network error, wait for 15 seconds
2502:20141028:105730.374 resuming SNMP agent checks on host "ho-1-sw4": connection restored
2502:20141028:105733.387 resuming SNMP agent checks on host "lipeck-1-sw1": connection restored
2502:20141028:105734.398 resuming SNMP agent checks on host "n.novgorod-cc-c3750": connection restored

and looks like some of items don't recieved for a long time (bcause queue proxy queue for a day). this is only snmp item problem.

anyway. i try to get those items by snmpget/snmpwalk In loop and doesnt have any problem.

also i have tried many variations:
oracle linux 6.6 + zabbix_proxy 2.4.1 + vmware-tools drivers(vmxnet3) + esxi 5.1
oracle linux 6.6 + zabbix_proxy 2.4.1 + linux embeded drivers(vmxnet3) + esxi 5.1
oracle linux 6.6 + zabbix_proxy 2.4.1 + vmware-tools drivers(vmxnet3) + esxi 5.5
oracle linux 6.6 + zabbix_proxy 2.4.1 + linux embeded drivers(vmxnet3) + esxi 5.5
ubuntu 14.04 LTS + zabbix_proxy 2.4.1 + vmware-tools drivers(vmxnet3) + esxi 5.1
ubuntu 14.04 LTS + zabbix_proxy 2.4.1 + linux embeded drivers(vmxnet3) + esxi 5.1

and right now i trying to test on hardware server..

what kind of problem this can be ?