I have had this problem also, i’m not totally sure but i think it can be caused by strange characters in the permalink of the post.
Take a look, and clean any rare symbol like “%”, “$”, “&”, etc.
Guess only alphanumerics and hipons ( “-” , “_” ) should be used, wordpress sometimes puts strange stuff in there if your post title has them.
Also watch out for duplicate permalinks even if you use a /%year%/%month%/%day%/%name%/ structure.
