Adding elements to DOM with C#

Hello, all.  I've got an edit page that pulls information about an event from a database, then populates areas of the template page with the proper information using the C# code behind.  One of the elements I use is a span, which I will need to manipulate once the user clicks the "Edit" button.  My question is this: I was changing the innerHTML of DIVs in the C# code behind, but when I try to gather information from a DIV's child SPAN (using "document.getElementById('SPANID')"), I get the javascript error that an object is required.  In Visual Studio's debugger, I can see that the span is obviously there with the proper ID, but the Javascript can't seem to find the element.  Is the element not in the DOM because I haven't added it by appending children?  I didn't think this was the case because I'm 90% sure that I've modified dynamically created data that has been put in place effectively using ...