Check if your NAS device is connected to the Internet when the shared photos are being accessed.
Perform the steps below on your Frontview and report back your observations:
* Is your NAS setup with DHCP IP or Static IP? If static, do you have a Gateway and DNS setup under Network>Global Settings.
* Do you have System>Alerts Contacts setup as well, and receive those (you can Send a Test message there as well)?
* Also, does the 'Check for Updates' under System>Update work, or report connection problems?
* Does the firewall configuration block outgoing HTTP connections from ReadyNAS ?
Verifying the above things will help in narrow down any connection issues your NAS has with reaching the Internet.