In ProcessRobot, the "Terminate Process" Action can throw an "Access is Denied" error if the user that is chosen in the Process Properties Window's "Credentials" tab does not have sufficient permissions.
The error's cause can be traced in the machine's "Event Viewer", at the "Windows Logs -> System" tree.
The needed security permission(s) can be modified using the "Component Services" administrative tool.
It is important to note that any action should be performed by the local IT Department.
Finally, another user would need to be chosen in the Process Properties' "Override Credentials" tab in case the needed permission(s) cannot be granted.