Executive summary: if a comment fails to post, remove any HTML entities from it and try again; it should work then.
- Nothing happens; the reply form is disabled (buttons grayed out etc.), but the comment doesn't post.
- You get a message saying "Oops! Looks like Frank's nibbling on the wires. Please try again in a few minutes. If you continue to get this error, let our Support team know. (Frank tells us the servers are delicious.)"
The support team's aware of it, and the issue is mentioned on the list of known issues, although it misidentifies the problem:
Comments containing special ASCII characters (such as the 'hearts' character: ♥) are currently causing problems. Either the 'post comment' button will become grayed out, or you will receive a 'Frank's nibbling on the wires' error; in either case, the comment cannot be posted. Removing these special characters from your comment will allow you to post the comment. This issue is reported.
This isn't quite correct; it's not special characters that are broken as much as HTML entities. You can post comments containing the ♥ character itself just fine, but you cannot post the ♥ entity. That said, browsers and clients that convert characters to entities automatically will also be affected.