Buildout error while trying to remove add-on Products.EasyNewsletter

I did not need Products.EasyNewsletter anymore so I commented out the Products.EasyNewsletter line in buildout.cfg and ran buildout.

No errors were reported, but when I tried to start the site I got this error:

Traceback (innermost last):

Module ZPublisher.Publish, line 249, in publish_module_standard
Module ZPublisher.Publish, line 191, in publish
Module zope.event, line 31, in notify
Module zope.component.event, line 24, in dispatch
Module zope.component._api, line 136, in subscribers
Module zope.component.registry, line 321, in subscribers
Module zope.interface.adapter, line 585, in subscribers
Module plone.transformchain.zpublisher, line 113, in applyTransformOnFailure
Module plone.transformchain.zpublisher, line 85, in applyTransformOnSuccess
Module plone.transformchain.zpublisher, line 60, in applyTransform
Module zope.component._api, line 172, in queryUtility
Module zope.component.registry, line 163, in queryUtility
Module ZODB.Connection, line 860, in setstate
Module ZODB.Connection, line 914, in _setstate
Module ZODB.serialize, line 613, in setGhostState
Module zope.component.persistentregistry, line 40, in __setstate__
Module zope.interface.adapter, line 91, in _createLookup
Module zope.interface.adapter, line 439, in __init__
Module zope.interface.adapter, line 476, in init_extendors
Module zope.interface.adapter, line 480, in add_extendor

AttributeError: type object 'IENLRegistrationTool' has no attribute '__iro__' 

Opening the site in Zope throws the same error.

Re-enabling Products.EasyNewsletter in buildout.cfg fixes the error.

What am I doing wrong and how can I safely remove the add-on?

First uninstall the product from the site (from the control panel), then remove from buildout,cfg and rerun buildout. Also, read the issues before:

this can help.