Error using onnextbuttonclick event on code behind

Question

HI guys
 
I have a wizard control now i need to put some code behind the "next" button and am using onnextbuttonclick="OnNextButtonClick" 
 
<script  runat="server"  type="text/javascript">
     void OnNextButtonClick(object sender, WizardNavigationEventArgs e)
     {
         string fullname = txtFirstName.Text + " " + txtSurame.Text;
         txtEmpFullname.Text = fullname;
     }    
   </script>

to work with the "next" button...
 
Is the a way i can use this event "OnNextButtonClick(object sender, WizardNavigationEventArgs e)"
on my code behind page with out using javascript?? Because now the javascript is on my client side.
 
I get this error when am using the event on code behind "Compiler Error Message: CS1061: 'ASP.administration_frmemployee_aspx' does not contain a definition for 'OnNextButtonClick' and no extension method 'OnNextButtonClick' accepting a first argument of type 'ASP.administration_frmemployee_aspx' could be found (are you missing a using directive or an assembly reference?)"