Okay so I tracked this down this morning.
It's linked to the uiConfigurationNode.
Open up the file in a text editor, and search for "uiConfigurationNode" without the quotes.
Delete the entire definition for this node, it's quite a bit of text:
Your line numbers will be different to mine as I stripped a different scene right back.
Save the file, open up a fresh maya, and then open the scene. The problem should go away