WebLogic Portal (10.3.0) requires feature "com.m7.nitrox (1.0.20)", or compatible.
This is a bug, CR379999. that will be fixed WLP 10.4. In the meantime, here's the workaround from the bug report:
Download the plugin manually, and either 1) create an extension location on the file system from it and add that via Help|Software Updates|Manage Configuration, or 2) extract it to one of the workshop eclipse folders (i.e. tools/eclipse_pkgs/2.0/eclipse_3.3.2, tools/eclipse_pkgs/2.0/pkgs/eclipse, workshop_10.3/workshop4WP/eclipse, wlportal_10.3/eclipse).
Additionally, you can comment out the com.* import lines in your %BEA_HOME%\wlportal_10.3\eclipse\features\com.bea.wlp_10.3.0\feature.xml, like this: