More often than not, if you are unable to post to the wall it is because you have reached the maximum number of posts for the application for that day. Facebook determines post and gift allocations.
The limit right now is 10 posts daily per user, per application. If you post more than this the stories will not post. Please check that your permissions to allow posting from the application you use to play Zoo World are set properly.
Here are links to more info about Privacy Setting and Permissions for Facebook posts: