It could be a broken login cookie - try logging out, clearing cached content for
ncap.cyclechat.net (specifically) and then logging back in again and ticking the box to remember login details.
If this doesn't work and the problem persists, let me know and I'll look into the login cache database table.
Also, as a side note, the post editor is set to save drafts every 60 seconds (disk icon on toolbar) so you may be able to recover part or all of your post by logging back in, going to the thread you were replying to, and clicking the reply button - which should prompt the editor to load any save drafts.
You can also manually save a draft at any time by clicking the disk icon and selecting
Save draft.