Issue running the code [question about an article]

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C#

ASP.NET

Hi dude!

Your article is interesting, but i'am having an issue running it.
I have downloaded the code and when i run using the master.aspx as start page i get this error:

Microsoft JScript runtime error: 'firstChild' is null or not an object

in this seccion of the code:

function FindTBODY(idGrid) {
    if (idGrid.firstChild.tagName == "TBODY")
        return (idGrid.firstChild);
    // there is a caption, so go down one more level
    return (idGrid.firstChild.nextSibling);
}