AirPort Express Base Station "Guest" network does not allow logons. (spinning wheel)
The problem is the bridge mode:

From Apple Support:


  The DHCP and NAT option in AirPort Utility application > Network tab > Router Mode (default mode) must be selected on your primary base station (…)


If you had more than one Airport, all secondary stations must have Bridge mode on, given there is one Airport or Time Capsule working as the primary station.