I believe this line is the cause:
lblLeaveBal.Text = IIf(IsDBNull(dtEmp.Rows(0)("LeaveBal")), "00", dtEmp.Rows(0)("leaveBal"))
because you're using dtEmp.Rows(0) outside of the check that there are in fact dtEmp rows. Move this line within the if block
If dtEmp.Rows.Count > 0 Then
and the error should go away.
Good luck.