Still seeing some extra slashes from somewhere - if I click on your application's home link it goes to:
http://apps.facebook.com/thesillysausage// - note the double slash at the end there.
My guess is the setting in WordPress -> Settings -> WPBook:
Facebook Canvas Page URL, NOT INCLUDING "http://apps.facebook.com/"
You should have just
thesillysausage in that box.
But none of that explains why you can't publish to your fan page wall.
Here's a test for all the permissions. Go to http://developers.facebook.com/docs/reference/rest/stream.publish and find the "Test Console" at the bottom of the page. (Best to do this logged into Facebook as you).
Choose your FB application from the dropdown for "Application"
Enter "testing in console" in the "message" box - nothing for attachments or action_links for now.
Put your pageID (153157574708737) as the "target_id" and leave the "uid" field blank.
Hit the "Call method" button.
This should either give you a result - a "stream id" (and a test post on the wall of your fan page) or an error - let me know what that error is.
If it works in the test console and not in production we may have a FB bug. (Though I can't imagine since it works well for others - more likely we have some other problem).
Is it possible that your web hosting server is unable to reach Facebook? Some hosting providers block outbound traffic from the web server.