Change
#nav a.enrol:hover { background-position:left -207px;}
#nav a.donate:hover { background-position:-100px -207px;}
#nav a.volunteer:hover { background-position:-198px -207px;}
#nav a.photo:hover { background-position:-298px -207px;}
#nav a.events:hover { background-position:-397px -207px;}
#nav a.contactus:hover { background-position:-496px -207px;}
to:
#nav li:hover a.enrol { background-position:left -207px;}
#nav li:hover a.donate { background-position:-100px -207px;}
#nav li:hover a.volunteer { background-position:-198px -207px;}
#nav li:hover a.photo { background-position:-298px -207px;}
#nav li:hover a.events { background-position:-397px -207px;}
#nav li:hover a.contactus { background-position:-496px -207px;}