EntityMalformedException

I added an Entity Reference field with an Autocomplete widget to a node type.

My plan was to use first node type to contain references to nodes of a different content type. The target content type was selected and the field correctly saves.

However, when I visit an node edit page to add the references data, I am greeted by the following message:
The website encountered an unexpected error. Please try again later.

The reports page has the following log message:

EntityMalformedException: Permission to create a node was requested but no node type was given. in entity_metadata_no_hook_node_access() (line 665 of /var/www/mysite/sites/all/modules/entity/modules/callbacks.inc).

The message suggests no node type was selected but I can assure you it was and I have triple checked.

Can anyone help please?