Plone 5.1.2.1 can't add images to front-page, KeyError: None

Plone Support
1

Fresh install, fresh new plone site within. Edit the front-page. Add image either from existing /images folder, or by performing upload to /images folder. Whether resized or left as is, uploads fine, shows up fine in edit window. Click save, then error.

If remove the images from the front-page (clicking back to the edit page, from error page), and click save, then no error.

Suggestions?

Thanks!

Traceback (innermost last):

Module ZPublisher.Publish, line 138, in publish
Module ZPublisher.mapply, line 77, in mapply
Module ZPublisher.Publish, line 48, in call_object
Module plone.z3cform.layout, line 63, in __call__
Module plone.z3cform.layout, line 47, in update
Module plone.dexterity.browser.edit, line 58, in update
Module plone.z3cform.fieldsets.extensible, line 65, in update
Module plone.z3cform.patch, line 30, in GroupForm_update
Module z3c.form.group, line 145, in update
Module plone.app.z3cform.csrf, line 22, in execute
Module z3c.form.action, line 98, in execute
Module z3c.form.button, line 315, in __call__
Module z3c.form.button, line 170, in __call__
Module plone.dexterity.browser.edit, line 30, in handleApply
Module z3c.form.group, line 126, in applyChanges
Module zope.event, line 31, in notify
Module zope.component.event, line 27, in dispatch
Module zope.component._api, line 139, in subscribers
Module zope.interface.registry, line 442, in subscribers
Module zope.interface.adapter, line 607, in subscribers
Module zope.component.event, line 36, in objectEventNotify
Module zope.component._api, line 139, in subscribers
Module zope.interface.registry, line 442, in subscribers
Module zope.interface.adapter, line 607, in subscribers
Module plone.app.linkintegrity.handlers, line 110, in modifiedContent
Module plone.app.linkintegrity.handlers, line 136, in updateReferences
Module z3c.relationfield.event, line 140, in _setRelation
Module zc.relation.catalog, line 539, in index_doc
Module zc.relation.catalog, line 469, in _indexNew
Module zc.relation.catalog, line 570, in _getValuesAndTokens
Module z3c.relationfield.relation, line 27, in from_id
Module five.intid.intid, line 41, in getId
Module zope.intid, line 84, in getId

KeyError: None

2

While I get this error trying to add any images to the default front-page, if I create a new page, I don't have any trouble adding images to the new page. It is just the default front-page that came with the initial install that is causing the problem.