If another one is attempted via DNS or alternative I.P. FileMaker will only permit one connection per client I.P. Many modern servers have more than one network connection and/or network I.P. Make certain your database is only being shared from ONE I.P. Your network configuration may well be very different to this but the problem may be occurring in a similar manner. You should also avoid connecting to a server hosted at 192.168.0.100 if that same server has not been configured to avoid hosting FM on 192.168.0.101. You can't open a file through and then reference it from another file via 123.45.67.89 (if that I.P. This means from 'Open remote' dialogue and from automatically referenced files in 'File References' also. You must ensure that all references to any database files you are trying to open are identical. If you are running FM Server then when this issue arises check to see if the client returning the error message is actually already logged in to the DB file you are trying to open. In my case it was a combination of DNS, I.P. It is caused by multiple connections between client & host.

It took a while to understand what was going on. I have had this issue under FM 7, 8 and 8.5 Windows & Mac with files hosted on FM Server/OS X Server. Today, I ran a script and it comes up that there is a licence conflict with another machine - the machine name it gives is my machine.

Filemaker pro license key conflict