There are a few reasons why this may happen...
1) There is a short delay between messages posted on Twitter and jotabl picking them up, have you waited at least 5 minutes for your message to appear?
2) Your message may have been deleted or you might be blocked by the shoutbox owner.
3) According to Twitter Support your message might not be picked up due to Twitter's internal quality filters, read this article for more information.

Log into your account and click the 'Message Control' option.

We don't need your password, just sign in by connecting your Twitter account to jotabl. All of your information is held private and sensitive information is encrypted. We will never EVER give out any personal information collected during your use of this site.

Please send an email to staff[at]jotabl.com.

Let us know on Google Groups or send us a tweet.