Puzzled - Permissions granted but Access Denied error generated

I'm puzzled.

I've created some content (in my role as administrator).

I've assigned one of my users to a "senior staff" roll that I created.

I've granted that role all permissions on the node module and most other permissions on most other modules besides.

When I log in as that user and try to edit content I created as administrator I get an Access Denied error when I click edit on the piece of content I want to edit.

That is to say, the administration functions are accessible, the content is accessible, the edit tab on pieces of content is visible and operable, but when clicked an Access Denied error page comes back.

Is there some permission I've omitted? Is content created by the root administrator a special case?

I've been poking around looking for answers in the documentation and forums, but haven't found anything that really answers the question.

I'm baffled. Please advise.