Quick answer

Go to Help → Install new software → Here uncheck “Contact all update sites during install to find required software”

Eclipse will prompt that the content isn't authorized or something like that. just ignore and continue. then everything will be OK.

At least this trick resolved my problems similar like this:

An error occurred while collecting items to be installed session context was:(profile=epp.package.jee, phase=org.eclipse.equinox.internal.p2.engine.phases.Collect, operand=, action=). No repository found containing: osgi.bundle,org.eclipse.emf,2.6.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.ant,2.7.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.codegen,2.8.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.codegen.ecore,2.8.1.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.codegen.ecore.ui,2.8.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.codegen.ui,2.6.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.common,2.8.0.v20120911-0500 No repository found containing: osgi.bundle,org.eclipse.emf.common.ui,2.7.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.converter,2.5.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.databinding,1.2.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.databinding.edit,1.2.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.ecore,2.8.1.v20120911-0500 No repository found containing: osgi.bundle,org.eclipse.emf.ecore.change,2.8.0.v20120911-0500 No repository found containing: osgi.bundle,org.eclipse.emf.ecore.change.edit,2.5.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.ecore.edit,2.8.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.ecore.editor,2.8.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.ecore.xmi,2.8.0.v20120911-0500 No repository found containing: osgi.bundle,org.eclipse.emf.edit,2.8.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.edit.ui,2.8.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.exporter,2.6.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.importer,2.7.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.importer.ecore,2.6.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.importer.java,2.6.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.importer.rose,2.6.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.mapping,2.7.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.mapping.ecore,2.6.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.mapping.ecore.editor,2.6.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.mapping.ecore2ecore,2.7.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.mapping.ecore2ecore.editor,2.5.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.mapping.ecore2xml,2.7.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.mapping.ecore2xml.ui,2.6.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.emf.mapping.ui,2.6.0.v20120917-0436 No repository found containing: osgi.bundle,org.eclipse.wst.common.project.facet.core,1.4.300.v201111030424 No repository found containing: osgi.bundle,org.eclipse.wst.common.project.facet.ui,1.4.300.v201111030424 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.codegen.ecore,2.8.1.v20120917-0436 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.codegen.ecore.ui,2.8.0.v20120917-0436 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.codegen,2.8.0.v20120917-0436 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.codegen.ui,2.7.0.v20120917-0436 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.common,2.8.0.v20120911-0500 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.common.ui,2.7.0.v20120917-0436 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.converter,2.8.0.v20120917-0436 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.databinding.edit,1.2.0.v20120917-0436 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.databinding,1.2.0.v20120917-0436 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.ecore.edit,2.8.0.v20120917-0436 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.ecore.editor,2.8.0.v20120917-0436 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.ecore,2.8.1.v20120911-0500 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.edit,2.8.0.v20120917-0436 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.edit.ui,2.8.0.v20120917-0436 No repository found containing: org.eclipse.update.feature,org.eclipse.emf,2.8.1.v20120917-0436 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.mapping.ecore.editor,2.7.0.v20120917-0436 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.mapping.ecore,2.7.0.v20120917-0436 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.mapping,2.7.0.v20120917-0436 No repository found containing: org.eclipse.update.feature,org.eclipse.emf.mapping.ui,2.7.0.v20120917-0436 No repository found containing: org.eclipse.update.feature,org.eclipse.wst.common.fproj,3.4.0.v201202292300-377F8N8s735555393B7B

Why not to use Eclipse Marketplace? Help -> Eclipse Marketplace... and then install Maven Integration for Eclipse and optionally Maven Integration for Eclipse WTP. It works for me.