Object reference not set to an instance of an object

Question

Below is the code that generates a run time exception in the subject line of this question.

        private void PopulateSummaryHeader(string empNumber, string fName, string lName, double hrsWorked)
        {
            lblEmpNumber.Text = empNumber;
            lblFirstName.Text = fName;
            lblLastName.Text = lName;
            lblDateRange.Text = "mm/dd/yy - mm/dd/yy";
            lblTotalHours.Text = Convert.ToString(hrsWorked.ToString("#.00"));
        }


"lblEmpNumber" is a defined in an .aspx page as follows:
<li><span class="label">ID:</span> <strong><asp:Literal ID="lblEmpNumber" runat="server" Text=""></asp:Literal></strong></li>
and is also declared in the aspx.desinger.cs

Is there enough information here to determine what I have done wrong?