What type of operation causes this message to appear?
Do you have more than one hard drive? If you have a separate disk for the OS and the FileMaker file you are using, both need to have space available.
Are you opening the file from a read-only disk image?
Could also be a permissions problem - try running Repair Permissions (Disk Utility)
I have an SSD drive with OS 10.11 and 113 GB available and a Data drive with 215 gb available.
This message comes up at random times when the computer is unattended. FM is always open but I am doing nothing. I am not opening any FM file.
Otherwise FM performs normally. There is nothing in the console log related to FM.
This happens to me regularly on a slave computer, which fires up a database via Task till Dawn, with a opening script that calls some statistic reporting in the database ending up with an email to the CEO.
The task is scheduled to run every Sunday.
The slave computer might be used during the week via TeamViewer by different people, who do some calcs and then do not quit Filemaker.
When they leave Filemaker open with the DBs open, my setup fails. Boss does not get his email and complains.
I connect to the slave and see exactly the same message you are seeing.
When Filemaker is not opened and gets into open state via Task Till Down opening the statistic database, everything works OK.
I do not believe any database is open when this dialog appears.