What's this strange error during entity_creation?
Argh, it seems the two different entity modules (core &amp; contrib) have confused me once again. 

The EntityAPIController I chose as controller class has no method save(). It uses entity_save($entity_type, $entity); instead.

So the function had to be: 

function my_entity_provision() {
  $a = entity_create('entityType', array(
    'pid' =&gt; NULL,
    'aid' =&gt; 1,
    ...

  ));
  entity_save('entityType', $a);
}