Current:

6.2.5. Remove a failed Instance
Cloud Engine can remove an instance object that has failed in a cloud.
Procedure 6.5. Remove a failed Instance
Click on the Instances application sub-tab.
Select the instances you want to stop using the checkboxes.
Click the Remove failed command button.


It should be noted that "Removing a failed Instance" does not remove the instance from the webui.  It removes the condor job from the condor queue, the object in the webui will be moved from "error" to "stopped"