[SNMP TRAP: 15006 in CPQCLUS.MIB]

Today I've tried failover the server to the other one. It's been failed all the time but not the disks or network adapter.
Just SQL engine and SQL agent..... I cannot find any answers online.......
So I was disappointed and want to reinstall it. When I did that , I found one thing was very interesting..
The DB that our junior DBA installed was not installed as the Failover node but a stand-alone...
OMG..