first of all, please check the WF, andcheck your SWFVISU settings for Leave request
Also, to which approver leave is sent? you should in his UWL!! Please make sure all customization are in place.
Please go through this
http://scn.sap.com/thread/2096541
http://scn.sap.com/thread/3300063
Please check all the absences ie counting rule etc