ISO: techniques for resolving "not a valid WDDX packet" errors

I used one of the internet's xml validation pages, where I uploaded the packet, preceeded by the wddx DTD. The packet is reported as being a valid wddx packet.

The site in question is a workflow/purchase request application. The applicant fills in the details, and the coldfusion bundles up the structure as wddx and wites it out to a database. Then, later, when the next person in the work flow needs to read the details, the database record is retrieved, the xml interpreted and the structure filled in, and then they can add details, provide approval or disapproval, update the record, and the request moves on to the next step in the work flow.

Just as you suggested, my first thought was to get at the data in question to see if I could determine what the problem is. I have tried the url 'directly' - it is the only URL I have for the operation. All I get, as I mentioned before, is a coldfusion message about the data not being a valid wddx packet.

What I need is some method of determining to what coldfusion is specifically objecting.

I'm not sure I completely understand the layout of your site or what it's trying to do, but WDDX is used for AJAX work (if you didn't know that already). Whenever I have trouble with wddx for ajax, I start by trying the operation itself (directly requesting the url), rather than trying it through the wddx call. It's usually much easier to find whatever error is occuring in the script being wddx'ed to.