esxi 5.1 snmp error

Hi

I have many 5.1 esxi servers licenced in a vcenter, some work with snmp some dont, the error I get is:

Agent not responding, connect uds socket(/var/run/snmp.ctl) failed 2, err= No such file or directory

I start the agent and after a few seconds it stops again with out of memory error

260GB ram 64 cores

Any ideas?