There are usually only a few reasons an embroidery machine can’t read the USB:
1. The USB is corrupt.
2. The embroidery file on the USB is the wrong format type for your embroidery machine.
3. The USB has too much memory (GB) for the machine.
4. The embroidery file is still zipped.
5. The embroidery design is too large for the hoop.
6. The embroidery file needs to be rotated to fit inside the hoop.
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For more detailed reasons and solutions for an embroidery machine not being able to read a USB, check out part 2 of this article.