Set Label Throwing Validation Error sometimes?

[sreephantom]

 I am using set Label api in my playbook to move the containers to a different label after playbook execution. It works on most containers but sometimes it will not move the container to new label.In the debug logs i could see set Label failed, Validation Error, failed to set Label..Can somebody suggest what the issue might be?

[Atriarc]

What commonality do the failing containers have with other failing containers, and how do the differ from containers that do not fail?