Hi Ian,
Thanks for your question. My name is Josh Wells and I am a support engineer on the Microsoft Dynamics CRM support team. I have reviewed your issue as well as Jason's response and the issue is going to be within the customizations.xml file.
If you haven't resolved the issue by now, my recommendation would be to export just the Account entity and no other dependencies. This would limit the amount of data you have to review.
Next, you would just want to look for <FormXML> and then review all of the "<Control id" sections. Notepad++ has a great functionality for finding all references within a document.
Hope this helps.