File "/opt/openupgrade-server/openerp/addons/base/module/module.py", line 426, in button_upgrade
raise orm.except_orm(_('Error'), _('You try to upgrade a module that depends on the module: %s.\nBut this module is not available in your system.') % (dep.name,))
except_orm: ('Error', u'You try to upgrade a module that depends on the module: mail_gateway.\nBut this module is not available in your system.')
according to the [docs](http://openupgrade-server.readthedocs.org/en/latest/modules60-61.html) mail_gateway is supposed to be covered