Upload broken after 4 -> 5.0.5 migration: Type error (Could not adapt)

After migrating from Plone 4 to 5.0.5, I cannot upload files.

Whenever I am on the Insert Image dialog, I click on the Upload tab, Browse for a file on my computer, and click Upload, the message "The file transfer failed" shows up under the file name (both if I try to upload to the current location or if I chose an other one).

Looking at the logs, I can see a TypeError: ('Could not adapt', <PloneSite at /Plone>, ):

Time
    Oct 10, 2016 06:49 PM
User Name
    robin (robin)
Request URL
    http://localhost:8080/Plone/@@fileUpload
Exception Type
    TypeError
Exception Value
    ('Could not adapt', <PloneSite at /Plone>, <InterfaceClass Products.ATContentTypes.interfaces.factories.IATCTFileFactory>)

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.app.content.browser.file, line 159, in __call__

TypeError: ('Could not adapt', <PloneSite at /Plone>, <InterfaceClass Products.ATContentTypes.interfaces.factories.IATCTFileFactory>)

Display traceback as text
REQUEST
form
file    <ZPublisher.HTTPRequest.FileUpload instance at 0x7f0719b60758>
cookies
__ac    'CFTjnTN5j0QRdXGUInlazrLkFjmZ4L4GSsmhUCm9AVs1N2ZiZTBmZXJvYmluIQ=='
plone-toolbar    '{"expanded":false}'
lazy items
SESSION    <bound method SessionDataManager.getSessionData of <SessionDataManager at /session_data_manager>>
other
AUTHENTICATION_PATH    'Plone'
TraversalRequestNameStack    []
LANGUAGE    'en'
AUTHENTICATED_USER    <PloneUser 'robin'>
URL    'http://localhost:8080/Plone/@@fileUpload'
SERVER_URL    'http://localhost:8080'
LANGUAGE_TOOL    <plone.i18n.utility.LanguageBinding instance at 0x7f071acc5440>
__ac    'CFTjnTN5j0QRdXGUInlazrLkFjmZ4L4GSsmhUCm9AVs1N2ZiZTBmZXJvYmluIQ=='
PUBLISHED    <Products.Five.metaclass.FileUploadView object at 0x7f071a15ac90>
method    'POST'
ACTUAL_URL    'http://localhost:8080/Plone/@@fileUpload'
URL0    http://localhost:8080/Plone/@@fileUpload
URL1    http://localhost:8080/Plone
URL2    http://localhost:8080
BASE0    http://localhost:8080
BASE1    http://localhost:8080
BASE2    http://localhost:8080/Plone
BASE3    http://localhost:8080/Plone/@@fileUpload
environ
HTTP_COOKIE    '__ac="CFTjnTN5j0QRdXGUInlazrLkFjmZ4L4GSsmhUCm9AVs1N2ZiZTBmZXJvYmluIQ%3D%3D"; plone-toolbar=%7B%22expanded%22%3Afalse%7D'
SERVER_SOFTWARE    'Zope/(2.13.24, python 2.7.12, linux2) ZServer/1.1'
SCRIPT_NAME    ''
REQUEST_METHOD    'POST'
PATH_INFO    '/Plone/@@fileUpload'
SERVER_PROTOCOL    'HTTP/1.1'
QUERY_STRING    ''
channel.creation_time    1476125312
CONTENT_LENGTH    '4086'
HTTP_USER_AGENT    'Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:49.0) Gecko/20100101 Firefox/49.0'
HTTP_REFERER    'http://localhost:8080/Plone/software-map/edit?_authenticator=b75e25ef4fc400935570092b7871806bfa970c6f'
SERVER_NAME    'XXXXX'
REMOTE_ADDR    '127.0.0.1'
PATH_TRANSLATED    '/Plone/@@fileUpload'
SERVER_PORT    '8080'
CONNECTION_TYPE    'keep-alive'
HTTP_X_REQUESTED_WITH    'XMLHttpRequest'
HTTP_HOST    'localhost:8080'
HTTP_CACHE_CONTROL    'no-cache'
HTTP_ACCEPT    'application/json'
GATEWAY_INTERFACE    'CGI/1.1'
HTTP_ACCEPT_LANGUAGE    'en-US,en;q=0.5'
HTTP_X_THEME_ENABLED    True
CONTENT_TYPE    'multipart/form-data; boundary=---------------------------6817814421939980424492295051'
HTTP_ACCEPT_ENCODING    'gzip, deflate'

How can I fix this and get the upload to work again?

Looks like dexterity types are not installed because ATContentTypes is getting used when it shouldn't be. It's trying to upload as an archetypes content type

Did the plone migration finish correctly?

I'm not certain why it isn't working for archetypes content yet though however; it should be degrading to that appropriate. Seems like the archtypes file factory isn't registered.

Thanks for your answer.
Indeed the plone migration succeeded. I don't remember the exact message but it looked very much OK.

If I look in the Add-Ons, I have plone.app.dexterity installed, showing up under Activated, and Products.ATContentTypes under Available.
I tried to install Products.ATContentTypes just now, didn't change anything. And then Uninstall, but still the same.

Now one more piece of information that may or may not be useful: In the Insert Image window (TinyMCE), I can't seem to get to existing images (in Internal Image tab). Everything looks empty. The images show up properly though, it's only that window, really...