SQL Agent won’t start on a Windows cluster for a particular instance
Seen in Windows Application log
Event: 53 Source: SQLAgent$CF3Common Category: Failover
[sqagtres] OnlineThread: Error 6 bringing resource online.
[sqagtres] OnlineThread: ResUtilSetResourceServiceEnvironment failed (status 6)
In Cluster Administrator, the SQL Server Agent had lost its dependency upon the SQL server resource for the affected instance.
Add the SQL Server dependency, bring SQL Server Agent online in Cluster Administrator