I just had the same issue with FMS12.
When you logon to your system once with the external link for example yoursolution.companyserver.com and then again to localhost:yoursolution filemaker understands that as two logons...although they come from the same machine. It kicks you out.
Filemaker should resolve this.
Having the same issue - how do I remove the references?
just wait for a minute or so and the server redraws the list of logged in clients.
afterwards pay attention always using the same way to login to your solution, so that fms does not get confused.
Same here, when using 1 x FMPa and 1 x FMS on the same Machine having 2 different IP adresses
The problem occured first time with FM12. Previously we had the exact same constellation:
Our Mac Mini has FMS running an 1 wLAN IP adress (192.168.1.21) and 1 Ethernet IP Adress (192.168.0.21) for syncing large amounts of DATA to another Mac (syncing has nothing to do with FM)
The same constallation works over years with FMS 11 and FMPa 11. After upgrading to FMS12 and FMP12a I always have to disable the Ethernet connection.
This just happened on my own small network (Mac Mini Server with FMS 12 Advanced and one client (me) running 12 advanced).
The IP conflict error message was with my static external IP address, not my system IP address. After burning a couple of hours updating and troubleshooting, I finally tossed the 'com.filemaker.client.advanced12.plist' from the preferences folder and restarted FM Pro. Worked fine, but I lost my list of Favorites - but found them in the corrupted file and copied them from there to reconstitute the list.