It could be another application is using the port FM is looking for. In your In your Sharing -> Instant Web Publishing menu, select Adnaced Options and change the Port number. By default 80 is probaly used. I believe 591 is reversed for FM. I am using 591. The only time I've have a problem was with both FMP10 and FMP11 running at the same time. Then the first one to start gets the port and I have to change it.
I cannot get far enough to turn on Instant Web Publishing so that I can access Advance Options. Doing a port scan, only port 5003 is used when FM is running.
When I try to startup by double clicking the database file FM hangs for about a minute and gives the same error. The file does not open. After I click off of the error message, I can then open the database from the OPEN menu. Still, I cannot access IWP.
I had tried IWP on both FM8 and FM11 free download.
Although FM8 initially worked, it did not after using FM11. I trashed FM11 and retried FM8 to no avail.
I redownloaded FM11 and it allows me to IWP. Still FM8 does not. I did not have a reason to upgrade to FM11, but now I do.