There is a bug in the current Google Analytics system. The problem is that when you create a new scheduled email report from the dashboard, you cannot add other reports in to it. If you try you get presented with the following error message:

No email reports appear in this list because you have not yet created any scheduled email reports. To create a scheduled email report, click the Schedule tab.

If you want to create multiple reports in the same email in Google Analytics, you need to go to the individual reports pages and create the email first, then go to each report page and add them individually to the email. If you create the first email report from the dashboard, then this is already counted as a batch report, so you cannot add anything to it.

There is nothing in the analytics system itself that warns you about this when you try to use it in this way, and it is very frustrating that it doesn't give any helpful infomation in the error message. I spent a good half an hour trying to figure out why it didn't work in the first place before I stumbled on the answer.