JoBills - another EYB member just emailed us about the same issue on her iPhone and this was my response to her:
If you are using Safari, check that you have Cookies enabled in your Settings. Click the Settings icon, then click Safari, then click Cookies and check what you have selected. I have Allow From Websites I Visit checked and I am always signed in when I go to EYB (which I connect to from an icon on my Home Screen - explained here in Help).
If you use a different browser, please email us with details and we will try to help you with those settings.