Whatever was causing my posting problem... this is a workaround for it.
If you are getting a “specified cast invalid” error when you try to post, and there's no apparent reason for it... try doing this:
- Make a copy (Ctrl+C is fine) of your post.
- Save a post with just a couple words in it.
- Go in to the Admin screen and edit that post.
- Paste in the previous post that would not submit.
- Save your post.
- Voila!
This happens to me more times than I care to recall. So far, my workaround has worked every time.