Windows Phone 8 won't remember my password

I'm using a Nokia Lumia 520. I've set up my iCloud account several times. My email address and password are fine. The mail client syncs all of my data once and then forgets my password. Instead of having my password in the space where it should be, it is replaced with a row of stars. The next time I try to access my mail or send a new message, it gives me an error message and the email goes straight into my outbox.

Any ideas?