The message is caused by the fact that you have a wrong version of Equinox (probably 3,5) included with your current Eclipse version. If you download the version 3.4.2. of eclipse (just follow the link from the Esbox installation_update site) the right version of Equinox (used by Esbox is 3.4) is included.

Furthermore be sure to have the same sites listed in the "available software" tab into your own list (otherwise other dependencies are not met) of available software.

After this, installing works just fine...

Good luck...