Rails - Jun 2006 - Lightbox and Prototype

I am running Rails 1.1.2 (frozen gems) and trying to use Lightbox 2.0.
I am getting this exception in Firefox:

uncaught exception: [Exception... "Could not convert JavaScript
argument arg 0 [nsIDOMHTMLDivElement.removeChild]" nsresult:
"0x80570009 (NS_ERROR_XPC_BAD_CONVERT_JS)" location: "JS frame ::
http://localhost:3000/javascripts/prototype.js?1151109408 :: anonymous
:: line 947" data: no]

Any help would be greatly appreciated.