If you see this error when trying to access a My Content Channel App from your admin account, your email address might be missing from the content manager settings.
To fix this:
Go back to the My Apps page and locate the app.
Click on the My Content Channel App you want to use.
Go to CONFIGURATION on the left side tab.
Add your email address to the reserved field.
Save your changes.
Once you've done this, you should be able to post messages, videos and PDF-presentations via the USE button.
Further instructions can be found here: My Content Channel - Add or remove content managers