The error in general means that your client code (eclipse) failed to validate SSL certificate that is provided by a server (marketplace). Ususally JRE is distributed with all major CA certs in truststore.
So on could experience issues when they work in corporate networks. In such case corporations often overtake ssl traffic repacking it with their own keys.
If that's the case, you can:
Use JRE that is provided by corporation. It should already have all the set up for handling MTM traffic
Ask your network admin to provide you root cert and install it manually
If that's not the case and in some reason you have no world's major CA certs in your trust store you can add server certificates one-by-one as soon as they are needed.
To do that you should open that https in browser, click "lock" icon next to your address bar and download the cert (particular steps may differ from browser to browser). Then install that cert to your trust store.
Here you can find the advice on how to install cert manually: https://stackoverflow.com/a/373307/8343843