Unable to get value of the property 'value': object is null or undefined

I have this code:
function ConvertWeight(form) {
document.getElementById("WeightInLbs").value = document.getElementById("WeighInKg").value * 2.2;
document.getElementById("WeightInKg").value = "";
}

And I get an error telling me that value is undefined but I can see it in the DOM tree.

Why is this happenning?

Welcome to DevShed, Nathe.

Please post the entire document.

It's a large document. The id's are valid text input tags.

Well if the code and references are valid then I suppose I am superfluous. If you want further assistance you will need to post the rest of the document. There is nothing wrong with what you have posted, so the error lies elsewhere.

I found a way around it. The code is embedded in a CFM file and JQuery has the same problems. I think it is a ColdFusion problem.