This error means that a job failed on 3 separate agents and the job caused the agents to become non-responsive. When this occurs, Electric Make fails the job and aborts the build. The build proceeds only if you have set -k, -i, or other options that allow the build to continue after an error.
This CloudBees Build Acceleration behavior is designed to prevent a single command from bringing down an entire cluster.
This message could be displayed if any of the following occurs:
someone restarts agents without disabling them first
an agent/host loses network connectivity
any other non-agent connectivity issue
For possible hints about why you received this message, examine the Messages tab on the Cluster Manager UI for the affected Agents when running that build.