Chaos Monkey Burn-CPU strategy : No credential or ssh agent found for root on node AWS EC2instance

I am trying to test an AWS Auto-Scaling Group by running Chaos Monkey's Burn-CPU strategy, to overload the CPU function of 1 random instance in the ASG. But I am getting the following error:

06:12:05.748 [pool-1-thread-1] WARN  c.n.simianarmy.chaos.ChaosInstance - Error making SSH connection to instance
java.lang.IllegalArgumentException: no credential or ssh agent found for root on node eu-west-1/i-325ebbcb
        at com.google.common.base.Preconditions.checkArgument(Preconditions.java:145) ~[guava-18.0.jar:na]
        at org.jclouds.compute.functions.CreateSshClientOncePortIsListeningOnNode.apply(CreateSshClientOncePortIsListeningOnNode.java:64) ~[jclouds-compute-1.9.0.jar:1.9.0]
        at org.jclouds.compute.functions.CreateSshClientOncePortIsListeningOnNode.apply(CreateSshClientOncePortIsListeningOnNode.java:40) ~[jclouds-compute-1.9.0.jar:1.9.0]
        at com.netflix.simianarmy.client.aws.AWSClient.connectSsh(AWSClient.java:755) ~[main/:na]
        at com.netflix.simianarmy.chaos.ChaosInstance.connectSsh(ChaosInstance.java:123) ~[main/:na]
        at com.netflix.simianarmy.chaos.ChaosInstance.canConnectSsh(ChaosInstance.java:101) ~[main/:na]
        at com.netflix.simianarmy.chaos.ScriptChaosType.canApply(ScriptChaosType.java:61) [main/:na]
        at com.netflix.simianarmy.basic.chaos.BasicChaosMonkey.pickChaosType(BasicChaosMonkey.java:141) [main/:na]
        at com.netflix.simianarmy.basic.chaos.BasicChaosMonkey.doMonkeyBusiness(BasicChaosMonkey.java:121) [main/:na]
        at com.netflix.simianarmy.Monkey.run(Monkey.java:134) [main/:na]
        at com.netflix.simianarmy.Monkey$1.run(Monkey.java:155) [main/:na]
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) [na:1.7.0_79]
        at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:304) [na:1.7.0_79]
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178) [na:1.7.0_79]
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) [na:1.7.0_79]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [na:1.7.0_79]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [na:1.7.0_79]
        at java.lang.Thread.run(Thread.java:745) [na:1.7.0_79]
06:12:05.750 [pool-1-thread-1] WARN  c.n.simianarmy.chaos.ScriptChaosType - Strategy disabled because SSH credentials failed

Why is this error popping up? Cheers