The error code ECP 20003 occurs when you are not able to update or reinstall the ESET product on your computer. The reasons for this problem could be another third-party antivirus software on your computer or partial uninstallation of a previous version of ESET. The instructions to resolve the Eset Error Code Ecp 20003 are given here.
Solution 1 - Uninstall the third-party antivirus software
Search for the other third-party antivirus software from Apps/Programs.
Select it from the Apps list and click Uninstall to remove the antivirus software from your computer.
You can even use the uninstaller tool if it is available for your antivirus software.
Solution 2 - Uninstall and reinstall the ESET product
Step 1 -Uninstall using the ESET uninstaller from Windows 10