Did you add the import plugins to eclipse? I have attached them. But you can find them here: https://www.cypress.com/products/psoc-creator-integrated-design-environment-ide
You can learn more about the error in the troubleshooting guide under section 6.1.2 here: Troubleshooting PSoC® Creator™ Issues - KBA217546
I had previously downloaded and installed the plugin linked to by PSoC Creator Help shipped with PSoC Creator 4.2 section <Integrating into third party IDEs><PSoC4 and PSoc5LP designs><Using PSoC4/PSoC5LP with third party IDEs><PSoC4/PSoC5 Eclipse Information><Eclipse installation & configuration> which was PSocCreatorEclipseImportJunoKeplar_4-13-16.zip into Eclipse Cpp 2018-12 which resulted in the error message I described.
Having now downloaded and installed the plugin attached to your message, Eclipse now works fine.
Many thanks for all your help.