Receive "ERROR: Maximum number of entries has been reached." assigning SSID to AP Profile

I'm trying to configure wifi on a FortWifi D90 and the only thing I'm trying to do is create a single SSID and bridge it to the LAN, so wireless devices are on the same subnet and have the same IP-scheme as LAN devices. There are NO APs in play, just the built-in wireless radio.

Here are the steps I have taken: 1) Created an SSID with the traffic mode set to "Local bridge with FortiAP's Interface".

2) Assigned the AP profile to the local radio. I made sure that the AP profile is using the D90 platform.

3) Finally, attempting to assign the SSID to the AP profile, produces the error "Maximum number of entries has been reached."

Not a very specific error, so I have no idea where to even start looking for the problem. So I have decided to seek an answer the Fortinet community. I did try creating an AP profile using a different platform and assigning the SSID to it successfully, but it doesn't work for obvious reasons (I don't have an AP attached that uses that platform), so it doesn't broadcast. Unfortunately, I inherited this issue from the previous I.T. administrator who sold them on the Fortinet D90. So I am hoping that I can just configure this appliance the way the client needs it.

If anyone can offer a reason why I am getting that error, information on whether the D90 is even capable of creating a bridged WLAN-LAN, or even a step-by-step on configuring this thing with a bridged WLAN-LAN- I would be greatly appreciative. Thanks.