Reagan Benjamin is correct.
Its a problem with subject. OP has written a long subject. That's because no one can't post reply.
I've tested that. I've alerted moderator for the post. Once subject got changed by moderator, then you can post your reply.
If you want to test it, then just create a discussion with same subject and then try to reply your own discussion. You can't post your reply. Then edit your subject (short it) and then try to post a reply. your reply will be posted.