I would strongly suggest creating a ticket with Tableau Support for this case.
yep, I agree with Tom, go open a case.
Or if you want to try and diagnose yourself, follow these steps:
1. Close TD
2. Clear out the logs directory - C:\Users\username\Documents\My Tableau Repository\Logs
3. Open your workbook and get the error
4. Look in the logs directory and the tabprotosrv log and see if it tells you anything interesting
Thanks for the suggestion and the log idea.
I'll raise a ticket then.