Your post is rather lacking in useful infomation but with a lot of guess work it sounds as if the owner of the service in question has blocked that IP address.
Without knowing what sort of internet connection you have there could be several reasons.
1. You have been making abusive posts or spamming the forum in question.
2. Somebody else at your workplace has been doing this.
3. Another customer of your ISP has been doing this.
4. The owner doesn't understand IP blocking and has made a mistake.
Any queries need to be directed to the owner of the site concerned.
