The communication error 21000066 on your EPSON printer can occur for a number of reasons. The most common cause are:
1. A faulty or incorrect driver being used.
2. A faulty or disconnected USB cable.
3. The printer not being powered on.
4. Network settings on the printer being incorrect.
5. The wrong port being selected.
It is recommended that you double check all of the above and verify that each one is working correctly. If everything looks to be in order, try uninstalling and then reinstalling your EPSON printer. This can help resolve any software or configuration issues.
If the issue persists, contact EPSON customer service for support.
