The E90 error on a Brother embroidery machine usually indicates a communication error between the machine’s computer and the control panel. Here are some steps to troubleshoot and fix the E90 error:

1. Turn off the machine and unplug it from the power source.
2. Check all of the cables and connections between the machine’s computer and the control panel. Make sure they are securely connected and not damaged or frayed.
3. Plug the machine back in and turn it on to see if the error has cleared.
4. If the error persists, try resetting the machine to its factory settings. Consult your user manual or the Brother website for instructions on how to do this.
5. If none of these steps resolve the E90 error, the machine may need to be serviced or repaired by a professional technician.

Possible causes for the E90 error can include damaged or loose cables, a malfunctioning control panel, or a problem with the machine’s computer. It is important to address the issue promptly to avoid further damage or complications with your embroidery machine.