So your monitoring sytems have grown and your zabbix started loggin "Zabbix icmp pinger processes more than 75% busy" at the dashboard.
All you have to do is open your config file (
/etc/zabbix/zabbix_server.conf) and find the a tag named
StartPingers. It'll be commented by default. Uncomment it and set it's value to something like 3 or 4. It should solve your problem.
### Option: StartPingers # Number of pre-forked instances of ICMP pingers. # # Mandatory: no # Range: 0-1000 # Default: StartPingers=4