Hi Carl
Are we talking controller based access points or autonomous?
For autonomous the SSID needs to be assigned to the radio interface and for multiple SSIDs you need to enable the broadcasting of multiple SSIDs.
For controller based systems when you create the WLAN you assign it to specific radio interfaces but there is no setting for broadcasting of multiple SSIDs - it's on by default.
Is this seen on all clients?
Have you monitored the air using a tool like 'inSSIDer'?
Regards
Roger