IPv4 address is being used by another interface or VIP

[jbgood]

I’m attempting to bridge LAN and WLAN,  and to allow wireless devices within the network to communicate with each other.

When I try to check the box for “Allow intra-BSS communication”, changes are not accepted and I get an input error:
This IPv4 address is being used by another interface or VIP.

2.1-RELEASE (i386)
FreeBSD 8.3-RELEASE-p11

LAN IPv4 set to Static 192.168.1.1
WLAN bridged to LAN
WLAN also set to Static 192.168.1.1
Both LAN and WLAN devices can reach out through the WAN.