Cisco :: 1252 LAP Won't Join WLC

I'm having an issue with a 1252 LAP that is connected to the WLC over a WAN link.Basically, it won't associate. The following is taken from a console into the LAP:
 
*Mar  1 00:00:07.799: %LINK-3-UPDOWN: Interface GigabitEthernet0, changed state to up
*Mar  1 00:00:08.799: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0, changed state to up
*Mar  1 00:00:26.851: %LWAPP-5-CHANGED: LWAPP changed state to DISCOVERY
*Mar  1 00:00:27.003: Logging LWAPP message to 255.255.255.255.

[code]..... 
 
The ap-manager interface is configured correctly and there isn't a duplicate IP address. The LAP was initially stand alone and was converted to LWAPP.The MTU over the WAN link is 1500 bytes.All I'm getting from the WLC debugs is:
 
Mon Jul 20 11:42:59 2009: 00:22:xx:xx:xx:xx Received LWAPP DISCOVERY REQUEST from AP 00:22:xx:xx:xx:xx to 00:19:xx:xx:xx:xx on port '29'
Mon Jul 20 11:42:59 2009: 00:22:xx:xx:xx:xx LWAPP Discovery Request AP Software Version: 0x3003300
Mon Jul 20 11:42:59 2009: 00:22:xx:xx:xx:xx Successful transmission of LWAPP Discovery Response to AP 00:22:xx:xx:xx:xx on port 29
  
So basically the join messages don't seem to reach the WLC. In fact they don't even seem to reach the local router on the remote subnet. The discovery packets are seen on the local router but the joins don't seem to appear at all.I'm not sure if it's a latency issue. Average latency over the WAN link is under 70ms.I'm assuming the certificate on the WAP is MIC and the MAC details have been entered into the WLC AP Security policies for authentication. I'm not seeing any debugging messages relating to bad authentication at all.I can't debug from the LAP as it's LWAPP, obviously.We're running WLC version 4.2.130.0.