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Try putting your code in the Page_Load event and see what happens.

Yeah, I already thought to try that. That had no effect.

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You are not able to use both single quotes and double quotes in a javascript statement, or you will receive the error.

Instead of...

document.getElementById("RBL_Firm").options[selectedIndex].value == '1'

...try this...

document.getElementById("RBL_Firm").options[document.getElementById("RBL_Firm").selectedIndex].value == "1"

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