IPSec VPN error in log 37130

Hi, I' m currently replacing our SonicWall VPN routers with Fortinet 50B units. At our head office I have done the switch to the new 50B. I have IPsecVPN tunnels setup to our two other locations and data is passing through without an issue. My only problem is that an error of 37130 keeps appearing in the Fortinet logs. There doesn' t seem to be a link problem as data and voice calls are working fine, but the error keeps appearing a couple of times a minute. error is: Message meets Alert condition date=2011-08-12 time=09:41:42 devname=BacchusMarsh device_id=FGT50B3G11607202 log_id=0101037130 type=event subtype=ipsec pri=error vd=" root" msg=" progress IPsec phase 2" action=" negotiate" rem_ip=***.***.***.*** loc_ip=***.***.***.*** rem_port=500 loc_port=500 out_intf=" wan1" cookies=" 17551550864f7a4e/3f0118ce04659fd0" user=" N/A" group=" N/A" xauth_user=" N/A" xauth_group=" N/A" vpn_tunnel=" BMtoSyd_Tunnel" status=failure init=remote mode=quick dir=inbound stage=1 role=responder result=ERROR Any ideas would be great.