Post Editor could not edit a post created by Site Admin, though permission had been given to the role explicitly for that post.
Resolved, for other's sake, posting the link to the solution at developer's forum:
For me, using WP 3.0.1, and Exec-PHP 4.9, Role Scoper 1.3.2
Must modify includes/runtime.php as follows:
$exec_articles_cap = ExecPhp_CAPABILITY_EXECUTE_ARTICLES; if ( empty($poster->allcaps[$exec_articles_cap]) )
fixed the problem for me.