Gary just upgraded to Windows 8.1 and he uses it to control his CnC machine for milling. He can write the data to the floppy, but the machine can only read the header and nothing else. Leo says that it could be that the upgrade broke the connectivity between the two and Windows 8.1 isn't compatible.
The chatroom says to make sure that in the BIOS, he checks a box that says "legacy floppy emulation." Leo isn't sure it will work, but it's worth a try. They also say that Microsoft turned off legacy support for some features in Windows 8.1. Leo says that the company that makes the software should know of issues and have maybe issued a fix. It could also be the the floppy disc that the sewing machine uses, has failed.