Access denied - how do I troubleshoot this?

I am trying to troubleshoot an access denied message when user tries to create an email. They get the typical (un)helpful pop-up:

Access Denied

You do not have permission to perform this action.

If you believe this is an error, please contact your Eloqua Administrator.

Well, that's me. But is there anywhere where I can see what is causing this error?

So far I have checked that the user's security group has at least view access to every asset in the email, including all dynamic content and images, header and footer. They also have permission to view the template the email was based on.