I tested on my iPhone 5 and didn't have any problems emailing a database. I'm using the newest version of Go 12.0.7. Also I understand that Go has a problem if several apps are running at the same time on your device. So you may want to besure all apps are closed except Go. If you still have problem you might try reinstalling Go on your iPhone.
I closed all apps, but it still didn't work, so I deleted and reinstalled the FileMaker Go app, and it worked fine. So thanks!!
One thing to note: I have had to delete and reinstall the FileMaker Go app a few times during this system devlopement process, as it seems to get put into some weird limbo state when you hibernate it for any length of time.