I created a workflow with just one scriptable task passing in "vcacHost" as the only parameter - and used your snippet for the scriptable task. However, it fails with the same error as well. See error below:
[2013-08-13 04:46:05.616] [I] Unable to convert org.mozilla.javascript.NativeDate into org.joda.time.LocalDateTime (Workflow:test1 / Scriptable task (item1)#17)
Added attachment (test1.workflow) Message was edited by: ahola