Hi
Yes, I am experiencing a similar issue.
Upgraded to 5.11 and am now unable to get an IP address via DHCP.
I am using an RB411 with two wireless cards, the second is in station mode and is set as a DHCP client. When I connect to my AP I remain at "Status: searching...". I know that the requests are being broadcast as I used the sniffer to see them. I also know that the DHCP server is working as it is giving addresses to other clients (both wired and wireless through the same AP).
The odd thing though is that if I connect to another AP which itself is a DHCP server I get an address. The only difference I can see is that in the first scenario the request is not handled by the AP but by another DHCP on the LAN.
Not sure what to try next but may see if I can revert to an older version.
I found a workaround to my problem:
1) Disconnect modem from RB450, then connect modem to another router
2) Reboot the modem, wait for it to assign an IP to the router (30 sec)
3) Reconnect modem to RB450
4) Power cycle RB450, wait for the system completely powered up
5) Power cycle the modem
DHCP Client is able to obtain an IP from modem again.