This looks like the type of issue you would get from a crash. Did FileMaker Pro crash shortly before this issue happened? If so, the server is under the impression the client is still logged in. Ask the server administrator to disconnect "you" from the server.
Well, I'm the server administrator, so I strolled over to see if I was logged in, and I am not. I then proceeded to log onto the server using Filemaker Pro 8 (which I still use since Filemaker 10 won't let me access server due to license conflict) and checked to see if my name showed up, and it did. So, with Filemaker 8, I can log onto server, no conflicts. With Filemaker 10 I get license conflict.
If it helps, I can launch Filemaker 10, no problem. Click to see the remote files on Filemaker server works OK. It's only when I actually go to OPEN a file on filemaker server that the license conflict message comes up. Thanks for your suggestions.
My experience isn't exactly what you are going through but I thought this might help:
I had a similar experience on my Mac with 10.6 SnowLeopard. After much emailing, phoning Apple, phoning Filemaker etc it turned out to be a bad performing plug-in that was not compatible with OSX 10.6.
As an aside, I think FM should have a more elegant way of trapping mal forming plug-ins than to lock the user out or otherwise prevent normal functioning)
This is my exact problem as well. What is the step by step solution?