I've just experienced something similar when modifying an existing post.
- modify post
- preview
- post ...
- took to long to respond so i cancelled in browser (firefox)
- tried to post again ... nothing happens ... preview works... try to post again ... nothing. Cycle can be repeated.
I managed to get out of it by pressing the home page (edits cancelled), modifying the post again and post (which then went ok on the first try).
PS: on previewing this post the preview box kep 'stuck' on with the message "Fetching Preview", so i finally opted to post without reviewing. Cookie issues ?