Exception 'TwitterException' with message 'Forbidden' i



I have a website built on drupal and I am experiencing some problems re posting to twitter. As the title indicates, I cannot post to twitter because i get an error as seen below:
exception ‘TwitterException’ with message ‘Forbidden’…

Can you help me find an appropriate fix for this if possible? If not, is there any other resource I can get my hands on to find a way out?