help with validation needed -> textboxID very complicated

Hello there
My friends wrote this piece of code and i need to test it, and i found an error in the program that when you don't enter anything in a textbox and save the values.
Problem is; i can't use ControlToValidate because it can't find this textbox control (because of a complex ID)
Here is the code:
 
<%
foreach (PackStudent student in GetStudentsAtKolegij(Int32.Parse(Request.QueryString["kolegijid"].ToString())))
{
 
 
%>
<tr< ...