I'm having a similar problem. I have my FM 11v.4 databases hosted on my iMac. I own 3 licenses and have a license for each of my Macs. When I'm connected to my local network (wirelessly) I can connect remotely to my hosted files on my iMac (one a 192.168.0.x) and not get the message about conflicting licenses. However when I connect to my iMac over a public IP (24.216.2xx.xx), I can see the files that are being hosted but when I try to open them, I get the conflicting license error and am forced to quit.
Also just FYI: I've alreay deleted all com.filemaker.plist files from my User's Preferences folder.
Thank you for your post, and I apologize for the late reply.
When FileMaker Pro launches, it reads the License Key and then searches the network for that License Key. If one is found, then the message above is displayed and it tells you where the License Key conflict occurred. In the screen shot above, it show that the License Key was found on "Todd Derek's 13-inch MacBook". Therefore, you will need to switch to your MacBook, and quit FileMaker Pro. If the MacBook is your current machine, then it is possible you crashed out of FileMaker Pro and restarted before the License Key could have been removed from the network. If after a minute you are still unable to launch FileMaker Pro, then reboot the MacBook and launch FileMaker Pro again.
I realize it has been almost three months, but if you have since found a resolution, please post here so others with a similar symptom can benefit.
I have discovered a solution to my license conflict problem - at long last! The conflict happened when I was accessing files from another computer in the office network, while my computer was in the office network (but not from home). The database file that was keying the conflict had multiple data sources, including some on my computer. External data sources can be seen and edited by going to File, Manage, External Data Sources. We cleaned up the data sources so it is only looking in one place for the file and the problem ceased. Hooray!