Tajima's USB readers are picky in well-documented ways. Run through these in order — the first three resolve roughly 90% of cases.
1. File system
Most Tajima models (TFMX, TMEX, TEJT) require FAT16 or FAT32. exFAT and NTFS are invisible to the machine. Reformat the USB on your computer (Windows: right-click → Format → FAT32; macOS: Disk Utility → MS-DOS FAT). Use a USB drive 32 GB or smaller; larger drives can have Windows-side trouble formatting to FAT32.
2. Folder depth
Tajima's file picker reads from the USB root or one level of subfolder. Files nested two or more folders deep are silently invisible. Move your .dst to the root, or to a single subfolder (e.g., /DESIGNS/yourfile.dst).
3. File name length and characters
Older Tajima firmware caps file names at 8.3 characters (DOS-style) and rejects spaces, dashes-in-some-positions, and most non-ASCII characters. If your file is named 'Customer Order #1247 — Bob's Towels.dst', rename to 'B1247.DST' before copying. Newer firmware (post-2018) is more forgiving but the safe path is short ASCII names.
4. Header check
A valid Tajima DST starts with 'LA:' followed by a 16-byte label. A 'DST' file that doesn't start with 'LA:' is something else with a wrong extension (a renamed PES, a corrupted download, an export from a tool that emits a non-Tajima-DST variant). Re-export from ValidStitch with destination = Tajima DST to be sure.
5. Eject before unplugging
Unplugging the USB without ejecting can leave the file system in an inconsistent state. The machine may see partial files or refuse the drive entirely. Always eject (right-click → Eject on Windows, Cmd-E on macOS) before pulling the drive.
If a fresh USB also doesn't work, send support the machine model + firmware version (LCD → Setup → Version) so we can confirm whether your firmware has a known controller limitation.