The E64 error on a Brother embroidery machine indicates a problem with the upper thread sensor. Here are some steps you can take to fix the issue:

1. Turn off the machine and unplug it from the power source. Wait for a few minutes before plugging it back in and turning it on again. This can reset the machine and clear any temporary glitches.
2. Check the embroidery hoop. Make sure it is properly attached to the machine and that there are no obstructions or interference.
3. Check the embroidery design. If you are using a pre-loaded design, make sure it is compatible with your machine. If you have created your own design, check it for any errors or issues.
4. Check the upper thread sensor. Make sure it is clean and free from any debris or dust. If it appears to be damaged, it may need to be replaced.
5. Check the upper thread path. Make sure the thread is properly threaded through the machine and that there are no tangles or knots.
6. Check the tension settings. Make sure the upper thread tension is set correctly for the type of fabric and thread you are using.

If these steps do not solve the E64 error, it may indicate a more serious problem with the upper thread sensor or the machine’s internal components. In this case, it is best to contact a qualified technician or the manufacturer for assistance.