kar files are not openable if they are generated from actors.
By right clicking an actor and choosing 'Save Archive (KAR)...', I can save an actor as a kar. The kar will be accessible from MyWorkflows fold on Kepler GUI. But when I tried to open the kar from 'File-->Open Archive(KAR)', a dialog will show up saying 'The contents of this KAR are not openable'.
I guess it is because that 'File-->Open Archive(KAR)' will only open workflows. But the item name looks it can open any eligible kar files. I think a better name would be 'Open Workflow from Archive (KAR)', and the error dialog should have more information.
Also, now I know the 'File-->Save Archive (KAR)' item means to save workflows as kar and right-click 'Save Archive (KAR)' item only means to save actor(s) as kar. Yet it is confusing that the two items have the same name but different functionalities.