Running Filemaker Pro 11 and Filemaker Pro 11 Advanced under Windows 10 in compatibility mode for Windows 7.
Regardless of compatibility mode, FM11 is beyond end of life of support and is no way guaranteed to function on windows 10.
Also, in checking the available printers by opening Filemaker printer Setup, I can see several printers in the list that are no longer connected to the computer.
This is a windows issue, not a filemaker issue. Delete the old printers out of the control panel > Manage printers snap in and they will no longer appear in the system dialog for printers.
If you do not specify an output destination before saving a script or if the specified printer cannot be found when a script executes, the output from the script step is sent to the default printer. I would have thought that "Print" should have found the "Current Default Printer".
Unfortunately, it seems that FileMaker will remember the "last used" setting before you host a file, so it will continuously reset back to that printer each time you open the file, not to the current default printer used by the OS.
My recommendation (after first upgrading to a supported version of FileMaker) would be to integrate a printer plugin, like this one:
This will allow you absolute full control over setting printer settings via script, and it will end up saving you time and frustration trying to support your clients every time a printer is replaced. They offer a developer license and a trial that can be integrated to vertical market products. There's also a demo file so you can play around with it.