Hi Priya,
That's great news, if it works for type U then the workflow step is fine. Authorizations, which are sometimes misleading, could well be the cause after all.
Try an auth trace (ST02 I think, no SAP system to hand at moment). The problem with SU53 is it will only show you the last failed authorization and won't always pick up HR structural authorizations, which I suspect may be the culprit here. If you have any HR techies around, ask them about Structural Authorizations.
Regards,
Mike