Most of our network is 450/450i. We use the same SNMP community string throughout the network - it has an @ symbol in it. The 450i's and everything else take it just fine however the ePMP stuff won't accept the @ symbol.
Was able to fix this... here is a workaround if anyone runs into this.
SSH into the radio and run "config set snmpReadWriteCommunity YOURCOMMUNITY" or "config set snmpReadOnlyCommunity YOUR COMMUNITY". I did "config save" and "config apply" afterwards and rebooted the radios, not sure what the difference in save/apply is so just ran em both and all is good.